Sorry I didnt reply last night matey. It wouldnt have helped much anyway as I havnt got a clue whats causing it
I would suggest turning down sound settings as this seems to have a massive effect on frames per second.
Try having a play with these console commands too. it will give you a better idea of what is happening.
stat fps: Shows frames per second in the upper right of the screen over the word �Objectives.� Much more accurate than looking at the F1 screen.
stat net: Shows network connection statistics on the left of screen. Type again, or stat none to turn off.
stat game: Shows performance information on left of screen. Type again, or stat none to turn off.
stat hardware: Shows information on your computer on the left of screen. Type again or stat none to turn off.
stat render: Shows rendering information on left of screen. Type again or stat none to turn off.
stat all: Shows all stat information. Stat none to turn off.
stat none: Turns off any stat info on the screen.
getres: Shows screen resolution and color depth.
memstat: Shows information on memory.