Buffer Size Vs. Hardware, What's the deciding factor for lower buffers? Options

[stimpy]

Hi,
What is the most important factor in determining if a Mac can run the lowest buffers; for triggering drums (therefore needing the shortest latency times) etc?

Is it RAM size or CPU speed or Software/ Hardware configuration?

i.e. If I add more RAM will I get a better performance at the lowest buffer setting (instead of crackling) or is it simply my inherent system architecture?

Thanks.

Powerbook G4 1.5 GHZ 512MB OSX 10.4.8.
M-Audio Firewire 410
CubaseSX1 / Sampletank XL 2.2