JRockIt is the JVM from Bea, it is certified to be java-1.5 compatible and is heavily optimized for Intel/Linux. (Has NIO)
It can also choose the GC is uses at runtime, and determinds the algorythm best suited for each use...
I use it since it outperforms the SUN-JVM (server) by about 30% (also with Limewire) and as you can see I need every cycle I can get ;-)
Sun client-Jvm does really bad when it comes down to highest load...

I have to admit that I hacked LimeWire to run batched, since it runs on an webserver withought XFree (but a dummy X11), so I start every 500s a new search, wait 200s and start downloading all results.

Seems like Limewire was not designed for this, I end up with thousands of threads and extremly high loads...