F# vs IronPython: When is one preferred to the other?

While the languages F# and IronPython are technically dissimilar, there is large overlap between their potential uses in my opinion. When is one more applicable than the other?

So far it look to me like F# is computationally more efficient while IronPython inherits a better library from Python. I am happy to be corrected.

There is a somewhat relevant question is F# to IronPython/IronRuby as C# is to VB.NET? but most of the answers there are about the language paradigms rather than their actual applicability.

Edit: I guess I should add a bit more background. I have good experience with Python in general, and have just learnt F# after a few hesitant functional programming steps before, mainly in Erlang. I currently feel able to continue using either Python or F# in the future. I would like to decide which one I should use and where. For example:

1. Python has very good data structures as part of the standard library. The other day I needed an equivalent of Python's heap module and it is not available in the standard F#/.net library. Point for IronPython.
2. F# can be used to build more convenient libraries, easier to access from other .Net languages. So for a .Net residing library I would prefer F#.
3. Cross-platform development. IronPython is better here. F#/Mono is usable is a much smaller set of platforms and F#/OCaml compatibility is not easy to maintain especially in terms of libraries.
4. The IronPython interactive shell seems to me easier than fsi. YMMV.

So the question boils down to: are there any reasons, apart from a preference of one paradigm to another or some team or corporate preferences, that would make you pick F# rather than IronPython or vice versa? Assuming you are equally confident in both? Or are they exactly equivalent for all practical purposes?

Edit: Ok guys, it looks you have judged this to be a stupid question, downvoting it and the answers. But at least it is honest. So please just a hint. Is it impossible to differentiate between the two or am I entering into some secret taboo by asking this question? If it looks like a troll can somebody please inform me?