I'm a fight simmer, and have used Flight gear. The main top options now are MS flight simulator, with incredible vusuals, and Laminar's Xplane, better flight model, so good in fact, that Laminar has a version which is FAA approved for simulator hours for pilots certification, and still great graphics. Both are way, way better than Flight gear (which is truly amazing for a FOSS flight Sim.)

If flight Sims are key to your decision making, I would pay for X Plane, a pay once model, that runs natively in Linux, Windows, and Mac, then spec around that. Next decision for me would be the GPU. In Linux most people seem to recommend AMD. I haven't delved into the issue, since I've had AMD for a while.

My usual decision process is:

1- analyze needs (programs and stuff that are important).

2- budget.

3- decide general specs.

4- get the best power supply I can afford within budget, gold, active PFC, modular, etc. Spec for at least 20% more wattage than maximum projected consumption Do a bit of research, googling etc. Be wary of ranked lists from established publications, as they are often influenced by manufacturers. So many people don't understand that the PS is the single most important component to ensure that everything else works correctly. Forum/reddit threads are better.

5- a good case. Fractal is my current go to.

6- GPU

7- processor.

8- board, Ram, memory, SSD, cooling

9- yoke, joystick (hotas), and pedals. 10 - everything else.