For reasons that I will explain another day, I have been switching video cards around a lot between my home computers. When I built my HTPC in 2008, I chose a video card with the same chipset as for my main PC - one based on the nVidia Geforce 8600GT chipset cards. One board was from E-VGA, and the other from Palit. The HTPC is now running with a slightly slower, but cooler and quieter, PNY 9500GT. My main PC is now running with a much faster PNY 9600GT. The 3rd PC had a built-in video card on its XFX nForce 750a motherboard, and supported SLI. However, like most built-in video cards, it was relatively underperforming, and it only had one digital video output. I have a requirement for two DVI - one to drive my Gateway FDH2401 24", and a second one to drive the monster HP LP3065 30" LCD that's getting delivered on wednesday, to replace the CMV-221D 22" that I sold last friday.
So, in this 3rd PC, I disabled the built-in video card, and after mucking with the jumpers on the motherboard just like in the good old days of non-PNP ISA cards, plugged in both video 8600GT cards into their respective PCI-E slots.
After a reboot, I could see that the graphics performance went from 5.9 in Aero and 5.5 in 3D in the built-in Vista benchmark, vs about 4.3 for the built-in 750a. After enabling SLI, the 3D score went up to 5.8 . I guess it's a little disappointing to just go from 5.5 to 5.8, but it shows SLI is working. The 5.8 was the lowest of all scores - everything else was 5.9 . The other PC with the lone 9600GT gets 5.9 in both Vista graphic tests.
This was with a single Gateway FHD2401 display running at 1920x1200. The second HP 30" display will run at 2560x1600 when I get it. I hope the presence of two video cards will help the performance when it gets hooked up.