Apparently, if you're on version 1.0 of the game you don't get flickering. But then again, you can't play multiplayer. What you do is, once you've installed and updated to 1.1, insert your Crysis 2 disc. Navigate to bin32 on the Crysis 2 disc and copy it to your desktop. Now rename your version 1.1 Crysis2.exe to Bioshock.exe. Now put the version 1.0 Crysis2.exe into your bin32. Use Crysis2.exe for singleplayer, and Bioshock.exe for multiplayer. Unfortunately you can't play multiplayer with the Crysis2.exe, but you can atleast play singleplayer at full speed. I've done this myself and it's a good temporary solution until Crytek fixes this. Yes, I said Crytek, as I don't think this has anything to do with AMD or nVidia due to it working fine on version 1.0.

*Note, I've only tested this with Crossfire, not SLI. Let me know if it works.