Started playing this yesterday. Performance is reasonable: I basically get 60fps indoors and anywhere between 40-50 (depending on various effects) in outdoor environments. I am using the in-game SMAA, too, as it only appears to have a 2-3fps impact on my system and I haven't noticed any stuttering or instability with it enabled. It's a pretty shoddy implementation of AA, mind you, because there's still some noticeable aliasing in certain scenes, but it does make the IQ a little better at least.
Game seems decent so far, though I'm only part-way through the second chapter. Movement controls seem off to me, especially when stealthing.