I know Prepar3d is supposedly a modified version of FS X. Looks like they've upgraded the rendering engine to support DirectX 11. Wonder if they fixed the CPU issues. FSX really likes high clock speeds. Relic of the Pentium 4 days. It can run like a sick dog even on modern hardware because of that.
X-Plane is an alternative, but I found it a bit obtuse. Even it's starting to look a bit dated. It really loves beefy system specs too. Their recommended requirements are basically all the CPUs and VRAM you can throw at it.
Yes, FS is a very CPU orientated game. I know from what I read on Flightsim.com that even today's hardware still isn't enough for FSX. This is especially true with all the addons and really complex aircraft. I have FSX Deluxe, but my main sim is FS2004 since I have about 52 GB invested in it.
Prepar3d is based on FSX and although I haven't touched it I guess a lot of FSX aircraft, gauges, etc can be ported to Prepar3D. Lockheed is the maker of Prepar3D and apparently pilots use it to learn things. I read you can even get credits. It's the only FAA approved computer sim. I really don't see a diffrence between Prepar3D and FS2004 other than the way it renders with the GPU more than MS's sims and the graphic looks.
I love my gauges I have in FS2004 and I made Area 51 where Janet, and many black project aircraft including UFOs fly in and out of KXTA. So it's kinda hard for me to use FSX. I like the PMDG 737NGX for FSX though. Very feature rich. More so than the PMDG 737NG in FS2004.
I have flown in the live VATSIM which is a multiplayer environment with people acting as ATC. The rules are based on international standards. For some reason, taxing is the hardest thing for me. Especially at unfamiliar airports.
My two main aircraft that I fly are the Raptor F-22 and the Boeing 737NG. Sometimes the B2 bomber and the F-1117A. If I go long haul I pull the F-22 out of the hanger and climb up to around 45,000' and cruse and mach 2. LOL
Here's my F-22 landing on the south end of my own created Area-51, KXTA.
https://www.youtube.com/watch?v=9SQpIEyR81I
The cockpit is retrofitted with gauges for utility and I left some that resemble the real jet. It's unfortunate that the Dev for the F-22 didn't make the gauges like I would have liked, otherwise I would have kept them. Yes, that is a SANDEL ST3400. LOL
http://www.sandel.com/sandel-avionics-products/item/fixed-wing/st3400-3-ati-taws-rmi