Because of how this plays a 40 fps is totally playable, and you can achieve that by turning AI air traffic off and lowering airport clutter (though this does take away some realism), I found the AI air traffic popping in the cause of most stutters.
I was getting a really low FPS on high so tweaked a few things following a video and now I get between 40-60fps but the performance still isn't the best, maybe because I only have 8GB RAM.