The more the application (GAME) uses the memory rather than the graphics card the more benefit you will see.
Unreal Tournament and Quake 3 are two examples of games that are memory hungry.
so what you should look for is High PCxxx rating and low Cas2.
this applies for both SDR & DDR ram.
to give you an example,
my PC150 SDRAM running at CAS2 performs almost as good as DDR PC2100 @ CAS2.5,
according to the sandra 2001 benchmark.
and gives me about 5 extra frames per second in Unreal Tournament.
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