Ok first off we'll compare prices.
http://www.newegg.com/Product/Product.a ... 6819115026
Intel Core 2 Extreme QX6850 Kentsfield 3.0GHz 2 x 4MB L2 Cache LGA 775 130W Quad-Core Processor - Retail
$980
http://www.newegg.com/Product/Product.a ... 6819115027
Intel Core 2 Quad Q6700 Kentsfield 2.66GHz 2 x 4MB L2 Cache LGA 775 95W Quad-Core Processor - Retail
$540
http://www.newegg.com/Product/Product.a ... 6819115037
Intel Core 2 Duo E8400 Wolfdale 3.0GHz 6MB L2 Cache LGA 775 65W Dual-Core Processor - Retail
$245
now for some reviews.
http://www.legionhardware.com/document.php?id=714&p=3
Well that was the only one that I found that pits a quad vs the e8400.
As you can see the number crunching sections lean heavily towards the quadcore, but in gaming though there IS a performance gain it's not too incredibly much.
I would do more research into this, but I'm getting bored of it...
But to close what you can buy with the price differences.
Core 2 Extreme vs e8400
http://www.newegg.com/Product/Product.a ... 6814130319
EVGA 512-P3-N802-AR GeForce 8800GT Superclocked 512MB 256-bit GDDR3 PCI Express 2.0 x2
(~$520)
OCZ SLI-Ready Edition 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 1066 x2 (yes that's 4gigs of fucking ram)
http://www.newegg.com/Product/Product.a ... 6820227181
(~$212)
And you could still go buy a bigmac with whats left
Q6700 vs e8400 $295 difference
You could buy one 8800GT as referenced above for ~$260
Or you could get 4gigs of ram, as mentioned above.
Now as far as saying "future proof future proof future proof buy the damn quad core" I think 4gigs of ram and 2 8800GT's in an SLI would pretty much just blow what ever friggan benefit you got from buying a quadcore out of the damn water.
Save your fucking money go with a dual core and spend it on some REAL PERFORMANCE. Upgrade later when the price drops because Octal core CPU's have come out. (Hyperbole, but the point is real)
There, now SHUT THE FUCK UP ABOUT QUAD CORES.
