A lot of it depends on what your mission/expectations are. Even a Class D sim does not completely replicate flying the real aircraft, I think Ben Rich of the Skunk Works said that’s why they’re called Simulators and not Realators, and if you fly a sim too much you risk negative transfer because you’ve trained yourself to fly the sim and not the real airplane.
But if you’re looking for something fun to bang around with, I’d go with MSFS X Steam, and add on some scenery from OrbX,
https://orbxdirect.com/. They even have a RV-4 on there.
https://orbxdirect.com/product/vansrv4 and you can find other RVs via an easy Google search.
https://www.google.com/search?q=msfs+vans+rv&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari
Here’s an example of OrbX’s add on scenery, my SeaRey in the virtual world and in an OrbX add on for Skagit Airport:
https://seareybuild.blogspot.com/2017/07/is-it-live-or-is-it-memorbx.html
FWIW, I’ve been simmming since the days of Atari 400s, I currently run Steam FSX on a 12+ year old home built Windows 10 machine, system is on a 500gb SSD, FSX is on a WD 1tb drive, FS9 is on a second drive 1 tb drive, with a ASUS 1050 card and 16 mb RAM. (I have FS9 stuff I have not been able to replicate in FSX I still like to play with.) I’ve got the frame rate locked at 30fps, max ground detail, zero airborne traffic, light boat traffic (gotta buzz the Puget Sound ferries!), and zero ground traffic. It flys nice and smooth, when I need a break one of my favorite things is to take a RA-5 Viggie add-on aircraft up from outside my hangar and go buzzing around the Sound.
I don’t need to have bleeding edge tech to have fun, take a break from building and just goof around for a bit.