Yes, structs are generally very good because they are mostly monomorphized. I haven't tested lately if structs of the same size but different types will fully monomorphize or if they share code and so require a small dispatch table. There was a CLR release awhile back where they discussed sharing code in this way to reduce code bloat.

There are still a few pitfalls. Off the top of my head, accessing generic static fields, ie. static class Foo<T> { public readonly static T Member }. Mainly for non-struct members, this typically requires a hashtable-like lookup to resolve the offset for the.

Also, generic interface dispatch can't be monomorphized, ie. interface IFoo<T> { void Method<T>(T value); }, so this too costs more than a regular virtual call because it too requires a hashtable-like lookup to resolve the generic overload to invoke.

I wouldn't expect F# to be faster in anything actually, speaking as a .Net developer. OCaml is very well optimized and the abstract machine was well designed to have an efficient execution. Do you have any specific examples where the CLR is better?