Graham Dumpleton (creator of mod_wsgi)'s answer to "Compare nginx+Apache+mod_wsgi vs nginx+uWSGI?" seems relevant:
When you load your typical large Python web application on top of the
most popular WSGI servers, the performance difference isn't actually
that much and usually nothing to get excited about. Hello world
benchmarks like the one you quote are very misleading as they test a
very narrow use case and the configurations used are usually never
comparable. You should consider watching my PyCon talk which talk
about bottlenecks in web servers and web applications.
http://pyvideo.org/video/703/web-server-bottlenecks-and-performance-tuning
Given that the WSGI server is not usually the problem, you should just
choose that which you find easiest to manage and has the sorts of
features you think you will require. Then use benchmarking and
monitoring of that choice to work out how to set it up so as to
perform best for your specific web application. Even then, any
increase in performance or gains in user satisfaction are not usually
going to come from such tuning.