Sorted, that works a treat, I'd already set it down to 50 FPS, but being the muppet that i am, just hadn't ticked the box.
oops. The only thing left and it's not really that important, but when it's on a loading screen it bounces around like crazy (fine during the game tho, so i can live with it)
Just run another couple of games on it and it's running those ok, so may just be peculiar to the tomb raiders.