Did you plan support Fibers in sapi? What is Fibers? It is async no- blocking rails instances that can handle more that 1 request at the same time (no threads!). More info you can get here: http://blog.envylabs.com/2010/07/no-callbacks-no-threads-ruby-1-9/ I tested it with Thin and works greate - from 0.5 req/s (slow action) i get to 2.4 r/s on ruby instance. I'm consider to switch from sapi to thin if you not plan support it.