Just putting it out there for the next person who sees this :-)

F# 4.0 is not really out of date. The language is fairly fixed now--apart from fixing buggy behaviour actually.

Part of it is that the general ML syntax is pretty timeless--all ML books share this advantage. As for F# specifically, all the headline functionality--type providers, quotations etc.--has been there for a while. I expect books covering 4.0 to be remarkably future-proof.

Thanks!