I admit that for Company of Heroes I must use medium settings... I don't have dynamic shadows and lighting, play it 1024 x 768, but looks good altogether and once again it doesn't take anything away from the gameplay. With this kind of game, you rarely anyway have the time to look around closeup views on your units...
Have only tried it from a friend's DVD and have not decided yet if I will buy it or not... I have seen the price is already going down, saw today a collector's edition (the metal box) for 39 Euros. (Think it was 55 a few weeks ago when it came out.)
I also think it is important to keep your system fit and not let it become fat and lazy, which means regularly defragment disk, clean unnecessary files, clean and compact registry, etc...
To launch all my games I use a nice freeware coming from the flight sim community called FSAutostart. It stops all unnecessary programs, tasks and services, defragments memory before launching the program and restarts everything on exit. It frees up a lot of memory and ressources...