If I can run Crysis with everything including Antialiasing completely maxed out at great framerates, then I can run anything. And Call of Duty 4? Even at max settings on everything, that game runs like a Windows 98 game on my gaming system.
I used to use System Requirements Labs, but I stopped when I rebuilt my system a few months ago.
It means that's what kind of speed each game that you run is going to see. It happens really on when you have a dual core or higher. Right now, my gaming computer's processor is rated for 5 Ghz of power, though it is really rated for 10Ghz of power if you include the other two cores that the check didn't even bother with.
Another way of seeing what your computer has is just by typing in 'dxdiag' into the run command in the start up menu. Althouhg it does not tell you how much RAM or CPU is avalible at that very moment in time, you can work out how much you have avalible for game play by just taking away around 256mb for xp and your processes ect.
Just wanted to add to the conversation.