I'm looking to upgrade my computer lookin to spend about $400. I'm getting the Gigabyte GA-P35-DS3L motherboard for $80 on newegg, and I'm trying to decide which processor to get:
 
The Intel Q6600 2.4Ghz or E8400 Wolfdale 3.0GHz 45nm?. What Does the 45nm technology mean? I know it requires less power but what else?
 
I was going to get the Q6600 Quad because I heard so much good reviews on how easy it is overclocking to 3.0 on air minimum with this motherboard. But I just now started to see the reviews on the new E8400 which sounds really efficient with 3.0Ghz stock but is only dual core.  I'm just planning on upgrading my processor for better fps in gaming and i need a new motherboard for more ram anyway.  
 
Does anyone got some advice for me or know which processor is actually better?  This is my first time build and would love to hear some feedback. I appreciate it.

45nm basic generate less heat and require less voltage, if they both run 3Ghz, then performance is about same, but E8400 can be OC over 4GHz, i choose e8400 over Q6600

I'm getting an E8400 tomorrow and a quad in a years time when they're potential is used more.
I don't know what you want it for but i'd guess you will never push even a duel core to it's cpu limit weather encoding or gaming etc.

Gaming: E8400
Video editing: Q6600

Cool thanks guys that was a fast response. Im all about gaming so ill get the E8400 and overclocking that sucker.  
I guess Quad Core is just for multiple programs and Dual core is all u need for gaming then i'm assuming. If anything I can get the E8400 and upgrade to Quad later on with this motherboard probably.  
 
Follow up... I just checked amazon and they're selling the E8400 for   $295! lol i guess b/c its sold out on newegg.
 
http://www.amazon.com/Intel-3-00GH [...] 310&sr=8-2

I have an E8400 on b/o at buy.com for $210 ... I suspect they are not anxious to "clear" this b/o at that price anytime soon.  But, they have promised to sell it to me for that $.  So, it may be months before I get it ... will give the mainboard makers time to update their bios and versions.
 
Note:  If I see them cheaper, I'll of course cancel the buy.com order and do the right thing.

http://microcenter.com/search/sear [...] submit.y=4

What is the rest of your build? A GPU upgrade will usually give you more FPS than a CPU upgrade, with most situations.

Uhhmm ? not sure the advice given is quite the full picture, E8400 may be the best for gaming at this time, but as games become more multi core enabled over the next couple of years the Q6600 even at its slightly slower overclock speed of 3.6Ghz (compared to about 4Ghz for the E8400) could well overtake the E8400 in new game performance.

By which time the already aged Q6600 will have been superseded by the 45nm Quad cores.  

 
Right now i'm running this:
 
Processor: Amd 64 4200+ dual core  
Motherboard: Asus A8N SLi Premium socket 939  upgrading to an Intel 775
Ram: 1 gig (2x512)  (not worth upgrading with a 939)
GPU: 7800GTX
PSU: Antec 550w
 
I tried overclocking it to 2.6-2.8ghz  and ran games ok but when i tried to burn CD's it would stop halfway thru so I just reset my bios again cuz i needed more ram.

I run some very CPU intensive applications.  I have a Pentium D 820 2.80GHz.  Would the Core 2 Duo Processor E8400 make that much of a difference?  Task manager has my CPU usage from 45-85% at all times while my available ram never tops 50%.  Tx.

 
Yes. It will make a huge difference. I switched from a Pentium 4 EE 3.4GHz to a Q6600 and EVERYTHING is much faster. Intels new CPUs, basically any of the Core2 range, have a much better IPC(Instructions Per Clock) than the old Pentium Ds and Pentium 4's due to a shorter pipeline. Your CPU usage will drop a lot. Mine hits about 27% max when a game is loading and stays around 3% low and 15% high while playing the game.

 
It will be a few years before most games are optimised for quads instead of dual cores. By then, both the Q6600 and E8400 would be 'obsolete' and replaced by much faster processors anyway.
 
If you plan on doing a lot of video editing/encoding or 3D rendering software, then by all means, grab a quad. But for gamers? Spend less on a dual core CPU and put the money towards a better GPU instead.  
 

I dont play games on this PC - I run a new small hedge fund and this PC is used to run computerized backtests.  The calculations made every second as the program analyzes years of data, 1 trade at a time is mind blowing.  For this application, would the core 2 duo E8400 really make a difference over the d820?  Or should I wait till I can get a sick Quad machine?  Dont want to waste $ if its not going to really be a visable difference.

 
Are you serious?  I have a two pentium D machines around my offices I built, an 805 D and a 925D.  They are complete junk compared to a C2D.  My E8400 makes your 820 D look like an Abacus.  Play around with these comparision charts and see what up.
 
http://www23.tomshardware.com/cpu_ [...] &chart=416

badge - thanks a ton - I've been looking for a chart like that - off to buy a new CPU TX

Yes, but aren't more quad core games starting to come out?

 
Not really. The vast majority of the multithreaded games can only utilise dual cores. The UT3 engine is supposed to show scaling between 2 and 4 cores, but in actual gaming the gains are minimal, and a higher clocked DC can still beat a lower clocked QC.  
 
I think Alan Wake is the next 'big' title that is supposed to take advantage of quad cores but it's been delayed so who knows when it will be out.