People are using QFJ in production. See the mailing list archives for more details. I've done some performance testing and the results were reasonably good, but I don't plan to publish numbers because they depend so much on the computing platform architecture, the logger or message store used (database loggers and message stores will be relatively slow, for examples), the application implementation and so on. Your best option is to write your own test program that will give you numbers on your own platform and with a representative load for your application. Any other numbers will be have dubious value for you (and this includes the performance numbers the commercial vendors use for their marketing).