There is a good chance you won't even notice a temp difference at 375/1100. I would just give it a shot and run rivatuner and play a game for a while. Check you load temps and see if they're OK.
You will know you OC'd too far if you get artifacts or other instabilities.
i want to OC the video card, cause when i run BF 2 on its very highest setting's it shows a little lag and i am interested to see if OCing it a bit will settle out the lag.