I wrote a rubygem called cloudspeq (http://github.com/meesterdude/cloudspeq) that distributes rails rspec spec's across a bunch of digital ocean machines to reduce test execution time for slow test suits in dev.

one of the things I did that may be of interest is to break up spec files themselves to help reduce hotspots (or dedicate a machine to it specifically)

Not as complex or as robust as what they did, but it works!