unfortunately you are at the junction.

If you gonna get new processor, the new board will have PCI-e which will force you to buy new GC.

If you buy new agp GC, you cant use it when you upgrade to new processor as newer board using pic-e. also agp now cost more expensive then pci-e.

simply not worth it to get an old tech by buying new processor or GC.

get a nvidia sli capable card as you getting sli mboard. at least in future you can buy another nvidia card to do sli. unless you go sli now.

i am using 6800gs and the performance is quit good, but no sli option as i am using agp.