Hello. I just started the game (first level, patch 1.2, latest beta drivers) on GTX Titan. The framerate drops from 60 to 30 and back all the time. When I turn off vsync it drops to 45FPS in the same places. Does anyone have this issue? Thank you for help.

That's how vSync works. If the game is running at above 60 fps, it will lock it to 60 fps. If the game is running below 60 fps, it will lock it down to half the refresh rate i.e. 30 fps. You can lessen the issue by enabling Triple Buffering and/or Adaptive VSync via nVidia settings.

VSync is only recommended if you can stay above 60 fps 100% of the time, but even then most players leave it disabled because it can introduce input lag especially when combined with Triple Buffering.

What RESOLUTION are you running the game at? The only scenario I can imagine a Titan dropping below 60 fps at 1080p is on full Ultra + 8xMSAA...something is seriously wrong. Or are you running a 1600p/3-monitor setup?