the c# performance over mono is really different to the f# performance..while c# has a decent performance on mono, f# doesn't performance so well......
You can run F# on the old "stable" branch of Mono (2.10.x), but I'd highly recommend running Mono 3.0.x instead. The older version uses an older, simpler GC which works OK for C#, but which seems to have trouble with F# (which generates more G0 objects than C#). The new 'sgen' GC in Mono 3.0 is a huge improvement though, so you shouldn't see much (if any) performance difference between F# and C# apps.