There is one BLATANTLY OBVIOUS answer to why Crysis doesn't run well. I'd have thought a forum like this would have SOME people realise...
You see... this game is made by EA, notorious for highly unoptimized games, riddled with bugs and made of pure crap. Now months prior to the release of Crysis, EA touted "a computer with 3 year old hardware can run this with no problem". My ass. If EA had spent some time making quality games, then Crysis would be a much more enjoyable experience. Crysis at low detail looks worse than Far Cry at medium.
Death to EA, scourge and scum of the video gaming industry!
And to the racist note: So what? I'm Chinese, I put up with shit everyday in reality, and I'm always shifted to the American team on Chinese maps on Battlefield 2. In the end, NK and US team up and fight the aliens.
Oh and I almost forgot to say, Crysis was never optimised for SLI or Crossfire setups. Then again, the OP mentioned 3 way SLI. Nvidia has always sucked badly with multi GPU, and 3 way SLI is proven to be an epic fail. It performs slower than normal SLI AND eats up far more power. So I'm not surprised 3 way is an epic fail in Crysis. But also, EA never optimizes well enough so really... multi GPU is not the way to go, and this is compounded by bad drivers from Nvidia. In the end, no one will be able to play Crysis until we get a supercomputer from space.