The F# compiler is reasonably fast but depending on your code you may hit some performance bottlenecks. One such area is using reflected definitions, which cause additional metadata to be saved within your assembly. We are getting that slowdown with compiling some WebSharper code, and this is something we are profiling at the moment and will be working with the F# team to resolve.

I would imagine that the optimizations made by the F# compiler slow it down from what you might find in C#. In Scala's case, the compiler uses a plugin architecture that would slow it down considerably as it would then need to offer any number of additional options that would be unnecessary in a compiler that didn't allow for plugins.