I’ve been using flightgear for about a year, however it wasn’t a pleasant time. Putting aside the physics and flight models
I'm sorry you felt to stick with FG for so long despite the unpleasantness. Good you found X-plane 11 which seems much better for your needs.
Having said that, I concur with what others have said, i.e. the framerate issue is likely a wrong configuration at your end and maybe asking for advice earlier would have spared you some frustration.
For the record, the physics FG is able to simulate is much richer than what X-plane allows, but FG is the product of volunteers and you didn't pay anything for it, so you get the work of enthusiastic schoolkids alongside that of highly skilled engineers and scientists side by side when you look at aircraft in the repository - so you have to go looking for good FDMs a bit.
Anyway, if you're so much happier with X-plane, please spare us the sermon how unpleasant FG is, we generally find it pleasant enough for out needs. Thanks.