Warren, I have built every flight sim computer I have owned, and that has to be a dozen or so. If you have the tiniest bit of computer building savvy, I recommend you look into building one. If you don't there are people here who can help you. I remember Ted (TXNETCOP) use to build them for people. If he doesn't there are others who can advise you or build one for you. You will get more for your money.
Still the biggest factor in flight sim computer is the processor speed. Most people pushing high numbers and lots of eye-candy are in the 4 GHz range or better. I run a
i7-5820K Haswell-E 6-Core 3.3 GHz LGA 2011-v3 running at 4.1 GHz with a water cooler and two GTX 970 video cards. The only reason I run two video cards is because I am pushing a 1040p projector and five LCD monitors in a home build cockpit. I need the outputs.
I have my frames set on 30 fps and normally I am there or the mid-20s. I might also add that I am running a lot of Orbx scenery and several add-on programs for the cockpit and its gauges. My scenery sliders are mostly far to the right with the exception of water which is average. All of this off of one computer. In the past I used two.
If you are running more of an average setup, you may not need at much horsepower. Still, I would get as fast a computer has I can afford. In the flight sim computer, speed is still king.
Good luck, if I can help you, let me know.