Aye, prior to 190.62, I was getting about 4fps on the main menu when I had quad SLI enabled. I've gotten to play the game up to now by only enabling a single chip.
I experienced flashing black, white and blocky textures followed promptly by a CTD intermittently during my time with 186.18, but back then I was much less aware of all the proposed solutions, so I didn't use -winxp, for example. At present, I'm pretty sure that none of the command line parameters make the performance better or more reliable for me.
At least SLI for me with 190.62 means performance is not worse than with a single GPU enabled. I suspect that fix was achieved by Nvidia disabling any GTX 295 SLI in-game outright while they looked for the real solution.
Fortunately for us, it was another driver update / game patch a few months ago that made GTA IV's performance in Quad SLI on Windows 7 brilliant.
I understand it's a fair read, but if there are any other Quad SLI users out there with or without issues, it'd be great to have your experience backing up or contradicting my bug submission: http://dev-heaven.net/issues/show/3936 - they're likely to find the fix faster I guess, the more complete the information we supply them with.