Hi I just started playing AC:R and whenever I am on rooftops or certain places down in the city I get low framerats (24-29) and this is extremely annoying when I'm playing the game. I have fiddled around with graphics settings and I get the same framerate dips no matter what settings I use (also tried lowering resolution to minimum) I could play assassins creed brotherhood just fine withouyt ANY lag, and I can also play games like crysis2 without probems. I have the latest GPU update and also have the latest patch for rewvelations. My specs are the following

asus geforce 450 GTS
interl q6700 quad core
silverpower 650W
asus p5q-e motherboard
4GB DDR2 RAM