How would Call of Duty: Black Ops run on this computer?

Black Ops should run well as your computer exceeds the requirements, but some computers have serious stuttering problems or low frame rate issues. There is almost no way to tell if that computer would get the problems or not, as some high-end computers get it too as well as lower-end. I haven't played GTA IV on the PC, but I would suspect that it will run well because your system surpasses not only the minimum but also the recommended requirements of the game.