Quad core all the way, if you 5 box, you can set 2 accounts to have CPU affinity with Cores 1 & 2 and 3 accounts to have CPU affinity with Cores 3 & 4.

Nothing wrong with 2 GFX cards - I run two 8800GTs (not in SLI mode). Each GFX has it own monitor; 1 GFX runs my main, the other my 4 slaves. (And the new 280's are way too expensive.)

I don't recommend a nvidia chipset motherboard unless you want to do SLI and run Crysis. Too many peeps having too many problems (see my other posts for more info). An Intel X38 is nice and stable.

Oh, and you don't mention an OS, but I use Win Vista 64bit (Ultimate); as this lets me use my full 8GB of ram. A 32bit OS will have trouble with 5 wows as the OS also needs to address the GFX cards memory in its limited space as well...

Enjoy your spanky new machine