GMS engines are quite powerful -- possibly even moreso than the OS but they're also a little variable in quality and have had carb issues.

All the member of our club have now had a guts-full of GMS engines and won't buy another. Sometimes they run okay, but all too often they produce deadstick landings or suffer from fuel-surging in the air.

If you want to narrow the choice down to two, make it TT versus OS.