Hey folks, ive been struggling with this as well, i have an amd x3 440, with a hd7870, a friend of mine has the same on an i5, with a 7750.. i had the 12.10 cata drivers, and he had the 12.11 cata drivers, i installed the 12.11, and also installed the CAP addition.. not sure if that was needed in the end.. but when i checked the settings i found:
under Gaming -> 3D Application Settings ->
there is an option called Wait for vertical refresh.
If u set this to Quality, it means that vSync is Always On.
I think, the option for Vsync is bugged in game, cause it doesnt seem to work wether u turn it on or off... had same problems when i tried that..
Now that i turned this setting to Quality, for Always On, it works perfectly.
(u might wanna also turn on triple buffering, a bit lower.. although im not sure if that only works for opengl, but i turned it on as well)
Give this a try for yourselves, and let people know if u experience the same.
good luck, hope it helps.
ps: just read there is now a 13.1 driver... last night there wasn't.. perhaps this is enough.. perhaps the same option works there as well.