I find that I tend to judge my VR settings performance based on outside views, especially at low levels and looking down. Of course, this generally stresses frame rates more than if sitting in the cockpit.
I think this gives me an apples to oranges benchmark when judging my performance based on Youtube reviews and forum postings.
I’m curious as to what most people in this group do to judge their VR performance.
As a pilot I tend to fly inside the cockipt 
If the exterior view stresses the performance more than the cockpit view, i would say you may have an issue 
The cockpit view is always the most expensive one, because the computer had to render both the cockpit AND the external world. If course if you seat in the cockpit and look up to the sky, it will be lighter impact for the FPS than external view looking down at the city center…
My advise would then be to seat in your cockpit with your plane diving toward the city center. Then you get the worst situation, performance- wise.
But in a general way, you’d better focus your settings on the cockpit experience, since this is where you will spend most of your time anyways. Settings that improve the extremal view but makes the cookout unusable would be useless.
I mostly use cockpit view since this is the view I am in when using the sim.
But in reality, I would say, that a mix of cockpit and outside view, and also a mix of dense city areas and backcountry would be the best to juge. The sim can behave substantially different under these circumstances.