A 770 2GB is not built for 5760x1080 4xMSAA on crysis3's high texture usage. The poor scaling and high renderingtimes is due to the complete and utter bottlenecking of the memorybus and imageswapping in the GPU memory. You can see the 7990 with it's 384bit bus and 6GB (or whatever it has) surpass the 770 SLI which should be faster.
I still don't think you quite understand the subject. I suggest you look on wikipedia how vsyncing works. It would make it allot clearer for you. Because frankly i think i've digressed on the subject long enough .. (wasn't originally planning to)