Rather than give you a fish, how about I teach you to fish. The best one for performance is...
Because the best is whatever is slowing down your computer most, and making the other components wait. There's a program built into Windows you can use for a rough measurement of what is slowing your computer down: Task Manager. Give your comp the ol' three finger salute, ctrl-alt-del, and open up the task manager, and switch to the Performance Tab
- Current/recent CPU usage
- Current/recent RAM usage
- Current/recent Disk usage can be found by clicking on the Resource Manager button if you're running Windows 7 (and I think Vista?) If you're not, you can fall back on your trusty Mark-1 Human Ears to listen for normal hard-disk drives.
Now, leave the task manager running and start up whatever game you want to play better. Turn the settings up a bit, then play for a min. Repeat until you're not happy with your performance. Play like that for a minute so the computer can measure it, and remember to listen for the disk with your Mark-1 Human Ears, if you need to. Then alt-tab/close the game and quickly go back to the Task Manager, where you'll see the history of your recent playing. Whichever components are being used near or above capacity are the ones you can replace to improve your performance. And if they are all green, but your play experience was still choppy/slow/poor quality, then you probably need to replace the component we didn't measure: your graphics card.
(In the case of having to listen for your disk, you don't want it to be working all the time while you play, but that could be a symptom of not having enough memory, so upgrade memory first if it was all being used and the disk was always working.)
There are more involved ways to measure, but if its all you have, the simple Task Manager will get the job done.
Don't guess, don't have us guess, Measure.