A friend of mine purchased X-Plane 11, and wanted some help on how to start up, so I made the plunge and purchased it too to help him, and some day, hopefully fly together.
So what have I discovered? The KSEA area is a terrible performance drain, and in my opinion, a terrible location for a "demo" area, because as you can imagine from my first post here, I took it as the defacto performance I would expect from the simulator as a whole.
When I fly in the area I usually fly, which is Norway, even with third party scenery, I get far better and stable frame rates. I hover between 25-40 fps depending.
Yes, surprisingly, it's the same frame rate, more or less, as I wrote about in the opening post, but somehow it feels way more fluid and acceptable now than before.
Laminar, I don't know what you can do, but please take note of this.