My under standing with the 8rib solution, has to do with slip more than stretch.
This is why the LSA has a separate belt track, so they run a larger crank pulley and thererfore larger supercharger pulley.
The Gates belts are quite good with stretch from my memory while at GM Powertrain. The focus where was belt slip, not stretch.
I'll run the 6rib and see how it goes.

Also, I'll be running an auto, so no clutch assist for me.