First clarify that I took two days looking for a solution on the net and so far nothing.
I recently purchased this game on Uplay, and I have a performance problem. When I start playing, after a few minutes the rate of FPS, drops considerably to about 10 or 15. If I press Alt + Tab for go to the desktop, and then return to the game, everything is solved but only for a few minutes and then FPS fall again.
CPU: Intel Quad Core (8 threads) i7 875k @ 4.0 Ghz
RAM: Kingston HyperX 8GB DDR3
Video Card: Nvidia GTX 580 MSI Twin Frozer II
Nvidia Driver Version: 301.42
OS: Windows 7 x64