Legit Reviews tested the XFX GeForce 9800 GX2 Quad SLI Video Card
>> XFX GeForce 9800 GX2 Quad SLI Video Card Testing
NVIDIA has done a great job with Quad-SLI and with some driver improvements it should only get better. The XFX GeForce 9800 GX2 graphics cards running in a quad-SLI showed increased performance in every application we tested versus a single GeForce 9800 GX2, which is something that can not be said about the ATI Radeon HD 3870 X2 as they had some driver issues on Tomb Raider: Anniversary. We almost didn't include Tomb Raider: Anniversary in our testing, but our two store-bought DVD versions of Bioshock say they have been installed too many times, so this game was a last minute addition...
>> XFX GeForce 9800 GX2 Quad SLI Video Card Testing