I have this exact same issue: stuttering with motion smoothing @ 45 fps and relatively smooth 50-60 fps without. It is most pronounced, as you say, when looking off the right or left wingtip while simultaneously performing a brisk aileron roll. Slow rolls and other gentle maneuvers don't seem to cause much of an issue. It happens down low as well as at altitude. All in all, it is pretty much unplayable with motion smoothing turned on.
My specs are similar: i7-9700k @ 5.1Ghz, 32Gb RAM, 1080ti, Pimax 8k+
I agree that this is most likely a DCS issue as, I have no problems with *another WWII sim* with similar graphics settings and motion smoothing on.