Which version of Ruby? 1.8 or 1.9? With my own projects Ruby 1.9 performs much better. Lua is well known for being small and fast, so I doubt Ruby 1.9 would beat it... Nevertheless, it'd be a lot more interesting comparison that Lua vs Ruby ???.
LuaJIT 1.1.4 Copyright (C) 2005-2008 Mike Pall
ruby 1.8.7 (2008-08-11 patchlevel 72) [i686-linux]