As other people pointed out, LW being the fastest is all relative as performance can vary greatly depending on computer configurations. I, for one, find that LW can exploit the greater part of my bandwidth (if not all) and thus provide me with super fast downloads. It is indeed CPU-consuming, but aside from my Mac opening and/or running apps a little slower (just a little), I can't really complain about it.
And I also seen both Kazaa and Limewire in action and from what I've seen, LW is far superior.
Now, I know that upgrading to Panther might not economically available to everyone (sure not me, but I saved...), but you can still run Classic through OS X 10.2+, so you don't loose your previous apps and features. I strongly suggest that you do it...

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

"Raise your can of Beer on high
And seal your fate forever
Our best years have passed us by
The Golden Age Of Leather"
-Blue Öyster Cult-