It will depend on how high your monitor's resolution is. But at 1080p, Crysis 3 will need medium settings for sure (maybe take down individual settings a bit more) to keep frame rates above 30 fps. The good thing is Crisis 3 looks fantastic even at medium settings. Crysis 2 isn't as demanding until you add the DX11 and high-textures packages. Even then it isn't as demanding as C3.
Btw, they are both great games.