Ok... Having both trucks... I gotta shoot alot of ya down. Yes we have shared "platforms" and similar parts... But that's where it ends.
Everything about wheeling is different. The extended wheelbase is a good and bad. Depending on the lift... A standard lift (since alot of you know my Fronty isn't normal). You have a better chance of highcentering and snaging the rockers. The major plus... The wheelbase is alot longer than the typical Jeep like SUV that rolls trails and makes ruts that the X finds a chanlange... The Fronty won't even notice.
The Rear Ends are TOTALLY different. So lifts and options change dramatically. You can easilly get alot bigger in a Fronty (mine with a 10" lift). I don't think there is an X out there even close to that number yet.
Cabins... Pretty close to the same, the Fronty drives more truckish... The X, more Car/SUVish.
Gearing... The Frontier has different gears... The OR X is lower geared than the NISMO Frontier. So you'll get better gas mileage in the NISMO at crusing, but have more low end power in the OR X.
Handling... Again, The X feels more carish than the Frontier... The Frontier feels like a lowered Titan.
The suspension between the two... The Frontiers OEM leafs are worse than ours... they WILL flatten with shackles.
There are way too many differences for me to list... Most of the front end and engine is the same, but from the cabin back... Everything changes.
IMO... drive them both... if you can find a friendly dealer with a dirt lot that will let you play a bit... do it.
I'd take the X any day over the fronty... So the Fiancee has the Fronty and I got the grocery getter
-MadManX