FWIW. A few thoughts to consider while making up your mind (some echo other comments above).
To have a realistic chance of "seeing" a difference with your "eyes" (as opposed to "measuring" a difference), one needs about a 20 percent improvement in FPS -- or more. Even then, only games with minimum FPS numbers below about 20FPS will actually look different.
A better graphics card is most likely to show an 20 percent or more improvement in FPS. As an over-simplification, one buys the best graphics card one can afford -- then, buy the CPU and rest of the system with the money left over.
A 3.3GHz i5 is fast enough for current games.
Games are 32bit. Although a couple have a 64bit version (in addition to 32b), changing to 64bit OS won't directly help games much.
4GB of DDR3 RAM is enough for virtually all games (a couple use more). However, a 32bit OS will not access it all -- whereas, 64b OS will. So, in a small number of 64b games that need extra memory, 64b OS is better. And, if one buys a graphics card with more than 1GB of memory (say 1.5GB or 2GB as some now are), 64b will make better use of the extra graphics memory. But, will making the change improve FPS by 20 percent or more? Not usually.
Bottom line, a significantly faster graphics card is the most cost effective way to go. The difference will be somewhat visible only in games that run slow to begin with. Also, in the future, buy 64b OS versions.
Of course, if money is no object, simply buy the biggest and best of everything. But, for most folks, choices have to be made to stay in a budget.
Of course, at least one or two exceptions to every rule. However, the exceptions may or may not apply to your case.
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