Pattern matching with guards vs if/else construct in F#

Question

In ML-family languages, people tend to prefer pattern matching to if/else construct. In F#, using guards within pattern matching could easily replace if/e

Answer 1

I did some testing on a self writen prime number generator, and as far as i can say there is "if then else" is significantly slower than pattern matching, can't explain why though, but I as far as I have tested the imperativ part of F# have a slower run time than recursive functional style when it come to optimal algorithms.