cache, as mentioned, is important full stop especially in games (basically anything that needs fast access to memory), is more important on the current C2Ds and the north bridge setup.
You may be able to clock a 2160 to 6550 speeds but clock for clock the 6550 will win hands down in pretty much any bench mark you care to run. plus the 6550 will then clock higher.
Here's one lot of gaming benchmarks done recently. (also read the write ups around the graphs).
AnotherMartin 6,229 posts
Seen 6 years ago
Registered 15 years ago