Second the GA-X79 series. Also, the ASUS PX9X79 series.
You say you want "at least" 3 PCIe x16 slots. I assume you're not doing SLI since you're not a gamer, but good luck with finding something that will do x16/x16/x16 with 3 slots filled.Plenty of stuff will do x16/x8/x8 or x16/x16/x4.
You don't want anyone to tell you to replace the entire computer, but if you go to one of the current motherboards you may have to change the PSU and memory anyway, since you may require an ATX12V v2.3 PSU (the power balance across supplies is different) and memory will be way different, which is almost changing the whole computer :-).
If you mean you want a solution that stays with socket 775, then I'd simply suggest swapping out your 3GB for 4GB or 8GB on that motherboard, and see what happens. 3GB is an issue on that chipset for speed.
Last edited by Bushfiva; 25th Jun 2012 at 04:21.
Reason: Did a x16/x4 when I should have done an x8/x8