What is the added value for learning F# when you are already familiar with LISP?
F# has the benefit that .NET development (in general) is very widely adopted, easily available, and more mass market.
If you want to code F#, you can get Visual Studio, which many developers will already have...as opposed to getting the LISP environment up and running.
Additionally, existing .NET developers are much more likely to look at F# than LISP, if that means anything to you.
(This is coming from a .NET developer who coded, and loved, LISP, while in college).