It appears the gpu clocks get locked to a certain performance level, or the game simply isn't asking for more resources when in a low performance area. So because it can reach 60 fps in one area, it does not clock higher when in areas with sub 60 fps.
Disabling vsync in an area with 30 fps can make it jump to 50/60 fps. It seems that using fps limiter in settings works better than vsync in this game.
In catalyst it's set to let applications control vsync. Don't know much about vsync controls, but as i've never seen this behaviour before, i assume the game is responsable and not the driver.