Update: I missed an earlier blog post and the discussion that followed it. http://donsbot.wordpress.com/2008/05/06/write-haskell-as-fast-as-c-exploiting-strictness-laziness-and-recursion/ On 32-bit machines, -fexcess-presision makes GHC output faster (only 2 times slower than C instead of 5-10, in my tests)