You might consider using the IBM SDK. They have some performance tweaks for server operations - particularly with respect to handled connections. See http://www.volano.com/report/ to get a feel for what is going on. I'd try the 1.4 first and perhaps the 1.3 if that isn't satisfactory. O(r perhaps if you could get hold of JRockit ... something I haven't tried yet.
You might also want to have a look at the servlet container performance characteristics: http://webperformanceinc.com/library/ServletReport/