Did you try to disable v-sync completely?
v-sync together with a limiter won't work,well it won't do what you want it to anyways.
Other than that it would help if you would show us cpu and gpu usage or better yet monitor it yourself while playing.
If cpu usage reaches 100% (hard to believe for your i7) then raise quality and resolution so your vga will slow down your cpu,if your vga reaches close to 100% try lowering quality.
Or maybe it yust has a problem with hyperthreading,so if you like try disabling it,or force the game to run only on 4 cores through affinity.