Depends on your processor, and whether you use integrated graphics or not.
There's practically no advantage to running faster RAM these days, unless you are using the very fastest processor and you have money to burn. You can get an extra 15% out of a machine if you buy REALLY fast RAM and also overclock it too, but unless you already have the fastest processor available, it's always much better value to just get a faster processor in the first place. Modern integrated graphics in A4, A6, A8 chips really benefit from faster RAM, but those all use DDR3 so I'm guessing you don't have one.
The difference between 5300 and 8500 is negligible, especially for games, as long as your CPU supports PC2-5300.
I am fairly sure that all Intel Core2 chips run at either 1066 or 1333 and I'm pretty sure AMD's PhenomII/AthlonII also works with PC2-5300. Anything more recent and you'd probably be asking about DDR3 instead of DDR2