Is there any real benefit from combiningDDR3 1066& 1600Mhz 4GB each?

No, you never want to run different speed RAM at the same time.

Welcome to Tom's Forum!  

Yeah sure there's benefits from 8GB over 4GB in both Gaming and Rendering. You'll need a 64-bit OS to access >4GB of RAM.

However, mixing DDR3 1066 and DDR3 1600 is a problem and typically I warn against it, but it 'can' be done.

Examples:
1600 CAS 9-9-9-24-2T @1.65v ; CPU-z JEDEC (1066) 533 MHz 8-8-8-24 ; see -> http://www.cpuid.com/medias/images/en/softwares-cpuz-05...
1066 CAS 7-7-7-21-2T @1.50v
======================

1066 CAS 8-8-8-24-2T @1.50v ; per above
1066 CAS 7-7-7-21-2T @1.50v
======================
1066 CAS 8-8-8-24-2T @1.50v ; (LCD) WORST of each, slowest Frequency, highest CAS, and avg Voltage.

CPU-z -> http://www.cpuid.com/softwares/cpu-z.html

Installation:
1600 = Orange DIMM
1066 = Black DIMM or visa versa but same set = same color DIMM slots

BIOS:
DRAM Frequency -> 1067 MHz
Memory Hole Remapping -> Enabled ; 64-bit OS
DRAM Timing Configuration -> Both
DRAM Command Rate -> 2T
TCL -> 8 ; example only - please calculate per example
TRCD -> 8 ; example only - please calculate per example
TRP -> 8 ; example only - please calculate per example
TRAS -> 24 ; example only - please calculate per example

CPU NB Voltage -> 1.20v~1.25v
DRAM Voltage -> 1.50v~1.55v

Save & Exit = Yes

Thank you so much for the comprehensive reply. I am running Win 7 Ultimate 64bit version so there s/b no problem. I am still a little foggy on my understanding of how to set the settings up even though I've read up on the procedures, nothing seems to correlate in my head with what I see on the BIOS screen...I will try using your examples above to see how it works.
What would be the optimal setting (I know it's subjective, but give me a ball-park best scenario answer) on just the OCZ 1600mhz 4GB? I'm still learning...right now I have the standard 9-9-9-20-33-1T settings

{9-9-9-20-33-1T} is wrong for any DDR3 1600 MHz kits that I know, and so I would either look-up the 'OCZ' Part-number or look at the 800MHz/XMP-1600 column per the SPD tab in CPU-z.

That said, there's two ways to set the RAM for DDR3 1600, 'I' prefer the FSB method because it's easier to OC the CPU later.

Most PC3-12800 OCZ are higher voltage and lower CAS. Example OCZ3P16004GK - http://www.ocztechnology.com/ocz-ddr3-pc3-12800-platinu...
Example: 1600 MHz 7-7-7-24-2T @ 1.70v <- Rated

AMD Phenom II X6 1055T 2.8GHz
2800 / 200 = 14
2800 / 240 = 11.67 ; rounded up 12

12 * 240MHz = 2880MHz = 2.88GHz

BIOS: Refer to pages 3-12~3-17 in your manual.
AI Overclocking Tuner -> Manual
FSB -> 240 MHz
CPU Ratio -> 12
DRAM Frequency -> 1600 MHz
Memory Hole Remapping -> Enabled ; 64-bit OS
DRAM Timing Configuration -> Both
DRAM Command Rate -> 2T
TCL -> 7 ; example only - please confirm 'SPD' per CPU-z
TRCD -> 7 ; example only - please confirm 'SPD' per CPU-z
TRP -> 7 ; example only - please confirm 'SPD' per CPU-z
TRAS -> 24 ; example only - please confirm 'SPD' per CPU-z

CPU NB Voltage -> 1.20v~1.25v
DRAM Voltage -> 1.70v ; example only - please confirm 'SPD' per CPU-z

Save & Exit = Yes

Verify RAM with CPU-z Memory tab; DRAM Frequency = 800MHz {x2 = 1600} CPU-z reports I/O bus clock in MHz and that the CAS Timings are correct.

Next create a Memtest86+ CD/DVD from the ISO/zip file and run for 4 passes; see -> http://www.memtest.org/

edit - fixed typos

Thank you so much Obi-Wan Jaquith for the lesson, leads , settings examples, and most of all your time that you put in to draft your replies that have taught me so much more in so little time and more than anywhere else this newbie to OC has been. Your patience and excellent layout of the principles have now begun to stitch together the neurons so that I'm just beginning to grasp fundamentals of how OC'ing is suppose to be done and what inputs are put where. No place else I've been has anyone put it in such understandable terms, and for that you should be rewarded, but all I can offer is my gratitude and appreciation.
I had already gone and gotten the CPU-Z download after your first reply and that was where I copied my settings from on my last reply. I'm going to try your suggestions for the BIOS settings on the 1600mhz rather than combine the two for now. I can always play with that later. You've given me my first good answers on how to properly set my BIOS for what I have (which is the 4GB of OCZ3RPR1600C8LV2G which I just got for $30 last week). I've been searching for a week for understandable answers, and U-Tube, ASUS, and a couple of other places were all busts as far as trying to find out what goes where and how to input it. until I came here.
I haven't tried Memtest yet, although I did go to the download site and tried to figure out what I was suppose to do... and you've also kind of cleared that up for me as well.
So thanks for all your help and guidance. I will copy my CPU-Z stats and let you know how i did.
I'll put in a good word with your bosses if they haven't already read my wordy reply... sorry about that..I'm just thankful is all.
Take care, your humble newbie Padawan of OC'ing is off to experiment now...

Updated BIOS Settings and came up with this CPU-Z outcome:
http://valid.canardpc.com/show_oc.php?id=1981683

my only question is why is it showing MAX Bandwidth at 10700 instead of 12800?
(I did bump it up from 2880mhz core Speed to an even 3000mhz and it seems steady)

PS: Kinda feels good being labeled a "Youngster" here at my age...but I'm maturing quickly here!
Thanks All and Obi-Wan Jaquith!

Your RAM is actually OC 'above' (faster than) Rated; see -> http://www.ocztechnology.com/ocz-ddr3-pc3-12800-cl8-edi...
1600MHz DDR3
CL 8-8-8-24 (CAS-TRCD-TRP-TRAS)
1.65 Volts

*You used my example to the letter, but the differences are as follows:
TCL -> 8
TRCD -> 8
TRP -> 8
TRAS -> 24
DRAM Voltage -> 1.65v

IF Memtest produces errors then change the above (4) tweaks. Oddly, when you OC RAM above Rated you also need to increase the DRAM Voltage above spec (e.g. 1.65v->1.70v). IMO if it works then leave it  

This is the CPU's 'Rated Frequency' of DDR3-1333MHz "MAX Bandwidth at 10700 instead of 12800" ignore it - it's a specification not a reading. On some Intel it's 1066 (8500) and other CPUs it's 1333 (10700).

As I said, the FSB is the steps toward OC, if you set the CPU Ratio much higher you'll also need to manually adjust a few more things i.e. vCore 'Processor Voltage.'

Yep...I've been finding that out among the intermittent crashes of either the system as a whole, or on Mozilla more frequently.. I had to go back to the boring motherboard defaults to get stable again. But it's a learning curve that must be attained if I expect to get any respect from Oc'ing. Those "adjustments" as you call them sure are hard to hit upon when pulling it out of thin air...man, it was a good 2-3 hours before I got back my machine after having to reset the RTC Ram to get back on line. It's all part of the learning curve I suppose, but I'm learning! Now I'm back to square one, but remembered the settings for the RAM from the label at 8-8-8-24 1.65V but still ran across the dreaded blue screen a couple of times. I tried leaving all other settings on Auto after keying in your stats and mine and my experimenting, but it seems it wants more input and has less problems when I key in a figure close to what it wants - mostly by guessing I have to admit,. Now back to the beginning...the 8-8-8-24 1.65V and tghe other minor tweaks doesn't stay friendly long. I'm thinking of dropping the the other 4GB in and see how it fairs with it on slower speeds.

Here's the other way, see "Method #2" -> http://www.gskill.us/forum/showthread.php?t=7688

Otherwise you could try slowing the CAS using the FSB method I posted:

TCL -> 9
TRCD -> 9
TRP -> 9
TRAS -> 24
DRAM Voltage -> 1.65v

I have lost count of Post Failures and BSOD over the years...part of it!

Thanks my friend, I appreciate all the knowledgeable help along with the "hand holding guidance" you really didn't have to do, but that was just as appreciated, if not more for putting me on the right pat - to eventually drive myself crazy again solving these never ending puzzles that these cantankerous contraptions seem to get a kick out of throwing our way. Especially after we worked for hours in peace and everything was fine and dandy when we logged off and went to bed, only to find that it decided it wasn't quite as happy as we were and throws a totally unexpected tantrum by way of a never before seen glitch to start out our wonderful day.
It's been a pleasure Obi Wan.... I will let you know when I get stable and come up for air....but don't hold your breath...
Peace Out.....

To end this string seems appropriate to use my personal quote that ended up being sort of my mantra in life:

"The Glass is still Half Full, I just haven't figured out where they put it yet... "
by Casey F in San Francisco.
It's there somewhere tho...keep the faith...

Good Luck - let me know...

You might want to try DDR-1333MHz and run Memtest to see if the RAM itself is the problem. IF stock settings fail Memtest then the RAM is bad.

This is why it's never recommended to mix RAM...