Right, turns out the stutters were my own damn fault! 
During my tweaking for X-Plane, I had turned off hyperthreading, and apparently MSFS2020 really really really dosen’t like that! At least not on old 4 core cpu’s (i7,7700k)
Turned it back on again, and now I’m getting stable’ish 45-50 fps taking off from KSEA, on Ultra settings. No stutters what so ever, yeah!
My hope for running this in VR one day has been restored 
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