X-Plane's flight model works on a different system than most sims, as in simulating the effects of individual details of a plane, or so I've heard, which makes it easy to create a rather realistic flight model for user created fictitious planes, but hard to realistically match the dynamics of real world planes (and in your case, i really doubt the 50 hp difference would create a significant torque increase) Anyways, I don't see any reason why someone would choose it over FS9 (realism, great addons, community etc.).
On topic, i think IL-2 is the best WWII fighter sim out there right now. Although I did get a little annoyed at the difference in flight dynamics especially the seemingly incoherent mixes of yaw and roll at takeoff (countering torque pulling to the left with slight right rudder, ending up rolling to the right at just 50 knots?) and the tendency to immediately roll and spin in a stall (while in GA aircraft on FS9 you only get into a spin if you pitch up and use full rudder in a stall), I got used to it quickly and tend to stay away from the stalls. Other than that, it still is a lot of fun, and what I like most: challenging.