I've spent many hours trying to solve this problem, simply because I've experienced it at it's finest, silky smooth with no stutter at all, then BAM ! unplayable, for what I thought was no apparent reason, until now...
Try this, works 100 percent of the time for me.
1. Uninstall or at least disable Oculus Tray Tool (it does nothing you can't achieve by other, easier means)
2.Browse to C:\Program Files\Oculus\Support\oculus-diagnostics and run the OculusDebugTool.exe (make a shortcut on your desktop)
3. Set your Pixel Display Override ( I use 1.5 and can see everything clearly), and set Asynchronous Spacewarp to DISABLED.
4. Fire up X-Plane and go into the Steam VR settings on the grey box that pops up at the bottom of your screen, in the Performance tab make sure the two bottom check boxes have ticks in them, close the settings window, close X Plane and manually close Steam VR.
5. Back into X-Plane, load your flight and when you are in your plane move your head back and forward rapidly, if you see stuttering keep reading !
6. Stay in the plane, and in the Oculus Debug Tool that's still running on your desktop, click on the Asynchronous Spacewarp tab, change from Disabled to FORCE 45fps ASW ENABLED.
7. As soon as you make that change you might notice your graphics card not working as hard, back in the plane move your head about and you should be free from stutter.
The next time you want to run X Plane just start the Oculus debugging, disable ASW, start X Plane, get in a plane then Force Enable 45fps ASW, and you're good to go.
I've tried this with mostly planes that aren't certified to work in VR and it works perfectly for all of them, good luck and have fun, if it works for you please spread the word, it makes the difference between a rubbish experience and an outstanding one !