I just flew an hour in Orbx Florida HD with the TBM in B9. Was smother than ever. Had the stuttering before, but that was in 11.41 i guess.
But now even at Orlando with Detail on Max and frames dropping in the mid 20's, it was at all smooth..
So i can say it runs really well on my side. Seems not to be a general problem.
I also tried different stuff to tweak X-Plane. In the end i noticed that i gain the most if i take it how it is. Tweaked the NCP, noticed that X-Plane runs best with no custom settings in the NVIDIA CP. Tried different tools the manipulate the LOD, in the end the Sim looked like shit.
I adapt my settings to what i fly. When i fly in the US, i deactivate all scenerys in Europe. Also i deactivate the Plugins that i don't need for that flight. And normally i reboot my PC ahead of starting X-Plane.
In the End i can say that the TBM (for me) is by far less Frame killing, as someone would expect, keeping in Mind the complexity. Some planes in my Hangar have kind of no complexity and system depth, but are heavier on the Frames in comparison to the TBM