With Dead Space 2 you're going to have to disable Vsync if you haven't already, both Dead Space games have a broken Vsync option that caps the framerate at 30FPS and sometimes causes the framerate to drop below that. Dead Space 2 is not a demanding game by any stretch, and you should be able to get way more than 30FPS.
Depending on your resolution your GPU may not be strong enough to max out Battlefield Bad Company 2. If you're trying to max it out at 1080p, a 5750 isn't going to be enough. With my 6870 I get around 60FPS in the quieter areas, and 30 to 45 FPS when the screen gets busy when the game is running on max at 1080p.
I don't know what DAOC stands for so I can't comment about that game.