avoid 8.1 SLI has major problems in 8.1 (atleast in surround via firsthand knowledge, as far as nonsurround only what ive read) I had to downgrade back to 8 lest lose my ability to play ffxiv with sli enabled.
Weirdest problem ever. Aside from the driver hangs and the missing textures on the desktop.. via RTSS my cards would all show as fully loaded and heat up (atleast via rtss) to unrealistic levels, yet I would get performance equivalent to 1 card (with 4). I downgraded back to 8 and now my cards are getting between 70-95% performance and it fluctuates as you would expect instead of being locked at 99 99 99 99, and whether those temps were right or wrong, I got no SLI indicator and the performance was indicative as well of no SLI. Now my temps are where you would expect 60-70 and performance is doubled if not better. (oh and I get the sli indicator lol)
Anyways, im working through email and PM with a CSR and a QA engineer at NVidia to sort it out, but it may not make it into this rounds driver release (dec 8) so all you can do is try and hope your game is one of the ones that work and put up with the non game related bugs for now. If your GOC (game of choice) doesn't work, downgrade like I did.
So far standard SLI seems the most stable. Tri and Quad are having the issues (I fall in the latter)