That's one hell of a surprise gift.
I don't have an X-65F or even used one, but I do have a TM HOTAS Cougar with the Force-Controlled Cougar mod installed, which gives me a rough idea of how the X-65F might feel like (other than that the X-65F doesn't move at all, not even a centimeter, and the FCC is likely more prone to jitter).
Trying to use it in something like IL-2 Sturmovik or Aces High will result in the aircraft "porpoising" a lot, oscillating up and down as I try to keep it steady. Those old warbirds are just far too twitchy for a stick like that, and I have no idea how this one demo video of IL-2 with an X-65F was so smooth and steady.
Falcon 4.0, on the other hand, works wonderfully. Part of it is that the F-16 has a force-sensing stick in the first place, so it's more realistic. But the other part is the FLCS keeping the aircraft steady and stable. There's none of the twitchiness inherent to old warbirds because of it, and as a result, flying with the FCC feels great.
DCS: Black Shark was more of a middle ground. Flying could be a bit unsteady, but the FLCS-ish systems do help a bit, and it's not as problematic for weapons usage thanks to the Shkval easily tracking whatever you designate or holding a given point on terrain.
You could just sell off the X-65F and use the proceeds to buy something with a moving stick (pretty much everything else that isn't a modded Cougar with FCC, FCC-2, or FSSB), or if you at least like the throttle and the stick for Falcon, then do what I did and throw in a Microsoft SideWinder Force-Feedback 2 if you can get one for US$30-50. Only 4 buttons and a single hat switch on the stick, but it's smooth, precise, has practically no centering force slop, and the X-65F's throttle has enough controls to compensate.