Can people give me some advice on whether you can play at too high or indeed too low a resolution whereby it affects your MP playstyle negatively?

I recently dropped from 1800 x 1036 to 1200 x 948 (or somewhere along those lines) and it does seem to be making a difference.

Also do people find the size of screen a hinderance? I play on a 42 inch lcd but have a sweet lil 24 inch aswell upstairs and wondered if the smaller one would be better at all? (I play on PC - consoles are for kids!)

Noob questions I know but the smallest differences can have the biggest effects!

Thank you for your feedback in advance.

I find higher resolutions make it easier to discern enemies from the background at a distance. It is also easier to spot clocked enemies. However, if you need a higher framerate, of course drop the resolution down. I play at 1920*1200 on a 24 inch LCD, and find that Crysis 2 is optimized well enough to give give me a constant framerate >60FPS, which in my opinion is perfect for online play.