The E8500 smokes the older quad cores and even the "Extreme" versions if you OC it just a bit. It's easy to get to somewhere around 4GHz if you read some posts and play around a bit. The 780 chipset is death though so you'd have to go 790.

Other than that, I'd go core i7 period. x58 is a stable (it seems) chipset and most boards run both sli and crossfire and are very cheap on the power. Cost for a good x58 mobo and an i7 920 is about $750 or so (with new DDR3). A tad steep but the fsb is gone and the #'s show it besting my oc'd 8500 by about 50%.

Three sticks of 1gb OCZ gold for the x58 chipset mobo are about $80 unless you want more speed, but I think that's quite sufficient to start out with. I'm upgrading to the i7/x58/OCZ next month. I'm still waiting for a bad post about the setup -- none yet.

sparkinark