3dmark06 7900GS SLI is slower than one GPU with x4 core cpu

This is baffling me. I had a score of 4673 with one GPU, added a SLI GPU and it dropped down to 3930.
CPU: amd phenom x4 9750 (2.4GHz), this is the B3 stepping - no TLB bug.
GPU's: evga 7900 with 256MB DDR3 at 256bit, 450MHz Core clock, 600MHz Memory Clock.
MB: Asus m2n32-sli deluxe

I can't picture my CPU bottlenecking it, but I'm not sure what else it could be. I have all of the settings to default on nvidia. The two 7900's are both new to me (used), I took my old one out only to confirm these are working, but all 3 are the same. Any ideas?