You've seen a lot of settings, good settings, but eating up your fps. I have also seen a lot of these and here I am posting a setting that is optimized for not only weak PCs, but it is not necessary to be the owner of a monster on which only Crysis 3 dares to lag.
With my computer: Pentium D 820 2.80GHz , 4GB, NVIDIA GeForce GT 430 I had about 18 fps.