Does anyone know of a good alternative to ab or httperf for load testing high-performance HTTP servers? With httperf I can't see to coax more than ~25,000 reque

Does anyone know of a good alternative to ab or httperf for load testing high-performance HTTP servers? With httperf I can't see to coax more than ~25,000 requests/sec out of my framework built on Jetty, but ab can easily do > 45,000 req/s. Both seem to be limited by the load generator, not the server.