I had heard a while back that some time around April 20th, Intel would start dropping prices on its processors, which has made me wonder... for a new system build, would a Q9450 be worth an extra $100-$150 over a Q6600?  This decision is pretty big for me, because it also decides whether I go with an nForce 780i motherboard, or an Intel X38.  The 780i would go with the Q6600, and allow me to use SLI.  The X38 would be for the Q9450, and possibly Crossfire. Which processor should I get for my new build?  Any help is greatly appreciated.

The Q9300 (even though smaller cache) overall performance advantage is about 7% more than the Q6600, according to this review. The Q9450 would be even more.
http://xbitlabs.com/articles/cpu/d [...] html#sect0

The Q9450 is about ~15% faster than the Q6600. It also runs a lot cooler than the Q6600, so it'll save you a few bucks off the power bill.
 
I still think the Q6600 is the better value though, some places have it for less than $200.

The Q9450 over clocks better than the Q6600.  If you over clock I would get the Q9450.

I have the X3350 and it's average temperature is 44C.
Before that I had the Q6600 (I still have the cpu) and it's average temperature was 38C.
So the die shrink in my personal experience has not reduced cpu temperature.  
Both the Q6600 GO and X3350 C1 (Q9450) are rated at 95 watts.  
Physically the Q6600 distributes it's heat output over a larger surface area when compared to the Q9450.
The Q9450 has extra SMID instruction and a higher FSB rating giving it a higher clock speed which gives it a higher performance rating.
 
You have the final choice. At the end of the day it comes down to how much money you can justify is fair for the product you are purchasing.

If you read the xbit review quoted above you will see the Q6600 overclocks better due to the higher multilier putting less strain on the FSB. However, due to the chips architecture it has the potential to overclock further but the rest of the PC components WILL hold it back. If you are just after a mild overclock and power consumption is a consideration the Q9450 or the cheaper Q9300 are both good choices.

zpyrd, power consumption is down significantly compared to the Q6600. The TDP may be the same but the Q9450 actually draws less than 65W under load whereas a Q6600 goes close to 95W. The temp differences could come down to temp sensors calibrated differently, btw are you running the same type of cooling on both CPUs?

Major_Trouble, that is true, though the Q9450 does have a higher multiplier than the Q9300, and should hit a higher overclock, all things considered.

With a good quality P35/X38 board a Q9450 should hit at least 450FSB or 3.6GHz. Granted a Q6600 can also hit such speeds but its slower clock for clock and would also consume a LOT more power since you would need to up the Vcore to around 1.4V, whereas with the Q9450 you'd most likely do 3.6GHz at or near default voltage.

Q9450 is bad for overclocking when motherboard fsb is the bottleneck. So, if you use anything other than x38/48 chipset board for Q9450, it won't clock as high as Q6600. 1600mhz fsb = only 3.2ghz for Q9450. With x38/48, it'll clock higher.

I've got Q6600 to 4ghz prime95 stable, on air cooling at 70/70/68/68 stablized full load, but only at a vcore of 1.65, which is far too high. Q9450, should do better vcore and temperature wise, if fsb is not the bottleneck.

So basically, it's all up to me to decide just how much I'm willing to spend.  If I can spend a little more, I should go Q9450.  If I can't, Q6600.  I do have one final question though: After thinking it over a bit, I'm pretty set on using a 780i as my final motherboard for my build.  It has absolutely every feature I need, including SLI, and I'd really like to just use one for my build.  Now, I just wonder if the 780i is capable of maintaining a high FSB when paired with good DDR2-1066 RAM.  Can anyone give me an answer on this?  If I were going for a Q9450, I'd want at least 450 MHz on the FSB, and for a Q6600, probably only 400 MHz. (Both will allow 3.6 GHz clock speeds)

780i runs at 1333mhz fsb natively, and can reliably oc to 1600mhz fsb (3.2ghz for Q9450, 3.6ghz for Q6600). X38/48 runs at 1600mhz fsb natively, and can reliably oc to 2000+mhz. 450x4 on 780i will not happen.

Shoot, that's what I was afraid of... Maybe I should start looking at reviews for some ATI GPUs, so I can go for an X38/X48 motherboard instead!  If only Nvidia and Intel could get along and allow SLI on Intel chipset motherboards...

Define "normal".

Why don't you just use single card instead? Graphics development moves way too fast for sli/crossfire to make sense in term of best bang for the buck.

 
When you hit your thumb with a hammer and scream "S#@# G@#%$ M#@ F#$@@#"...  that normal.

I guess you're right, but it's always been my mindset to think that you shouldn't waste the second PCI-E 2.0 slot by leaving it empty... Maybe I should start looking at faster single cards, like the 3870 X2, or possibly the ATI HD 4XXX cards.  Any suggestions?  I've had my mind set on SLI 8800GTS G92s for the longest time, and the only card that can match that is the 9800GX2... which also costs a fortune.

I think you should just save the money and get a single 8800gt or g92 8800gts for now. It handles well enough with current games. Then wait and see if the HD 4000's are any good when they come out. The current crossfire choices from ATI are not attractive.

 
What resolution do you game at? Unless its 1920 x 1200 or higher, you don't really need a multi-GPU setup for the vast majority of todays games, Crysis being the obvious exception.

Couldn't disagree more with you there chap.
3870X2's or 3870's in CF are pretty nice set-ups

I'll be gaming on a 24" monitor, 1920x1200 resolution.  Multi-GPU setups should help me out.  And right now, I'm looking at a Sapphire HD 3870 X2.  Should suit me well... at least until the HD 4870 X2 comes out.

ATI isn't at its best right now. hd3870 is only as fast as a 9600gt, for higher price. hd3870x2 is far more expensive, but only perform slightly better than a 8800gtx, or overclocked g92 8800gts. It has some compatibility problems too, like crushing UT3 at any resolution when antialiasing is enabled.

With hd4000s coming fast, this is a bad time to go expensive on ati. Supposedly, the hd4000s is ati's cure for Nvidia domination recently and ta