Sorry to bump an old post, but I have a similar setup and can't get SLI to work for me. Using the newer drivers (306.97) I get intense flickering, although I can tell SLI is working (almost 100% FPS increase, but unplayable). If I jump back to old drivers (275.33) the fickering goes away, but FPS is the same as 1 card. I've tried the latest betas, but they crash GW2 completely.
What NVIDIA drivers are people using for their 460 SLI setup?
6GB Mushkin Redline Enhanced@1910MHz CAS 8
MSI 460GTX TwinFrozr II SOC 768MB / EVGA 460GTX 768MB (SLI)
Use the new 310.57 BETA drivers. They fix the flickering (unless one of your GPUs is bad/overheating)
Also, make sure that you put the mode for SLi on Alternate Frame Render 1.