How do you intend to use the bike?

I preface what I'm about to say with the caveat that there are a number of very happy FX riders on TE who have not "outgrown" their bikes. There is nothing inherently limiting about a bike like the FX.

That said, I'm one who quickly went from the FX to a road bike. It took all of about two months if memory serves. Once I got my road bike, I never rode the FX again. Don't get me wrong, I think it's a fine bike. I just like my roadie that much more. I'd emphasize, though, that my roadie fits me and has a comfy ride. That's the key to the comparison.