Alan_A

Confirmed.  Turning off UTX road traffic improved performance tremendously.  It's still not perfect - some changes in road settings are probably called for - but at least I know where the issue is.
 
It's possible I'll have to make a personal choice about tradeoffs - as a low-and-slow (or sometimes low-and-fast, if it's a Spitfire), I like my road traffic.  Helps bring the world to life.  So I might need to swap back to Vector, where road traffic didn't cause me any performance problems, and live with the greater VAS demand.  Am not sure if I'll do that, but it's a solvable problem.
 
The good news is that MT6 is off the hook.  
 
So... today air traffic, tomorrow the roads...  B)
 
Thanks, guys, for your help.

Can definitely recommend the PFC Beech Yoke.  Better with the Hall Effect Sensor upgrade.
 
They also offer a throttle console with interchangeable quadrants, some of which are designed for GA aircraft.
 
I haven't tried their rudder pedals, but they come well recommended.
 
Hope this helps.

BTW, here's a link to the MeatWater voice packs. Big package - 10-part download. But worth it. Be sure to read the install instructions before you start patching.