I've been experimenting with a well run ST G90 and found some interesting results.

Fuel: Powermaster 10%
Prop: APC 14x4w

Stock configuration: rpm: 10,500

Swap carb to Magnum 91/108 rpm: 11,500
Swap stock muffler to Ultrathrust rpm: 12,500

Magnum carb = $37.00
Ultrathrust muffler = $74.00

Bottom line: The carb swap is a no-brainer ... for $37.00 add 1,000 rpm
The muffler is a little expensive but adds another 1,000 rpm over stock. If you have an old ST G90 laying around, give it a try. Transition is great with the Magnum carb. Power with both mods is awesome... and it sounds like a high performance dirt bike!

I am going to flight test the modified ST in my Aeroworks Edge 540T 40/60 tomorrow. AUW is 6lbs.

Flight Report #1:
Engine would not run consistantly. I believe the problem was too much boost/heat using the Ultrathrust muffler. The bench runs were great with that combo, however, it was a totally different story in the plane. By the way, I switched to a Magnum 91/108 carb which has proven to work very well in the G90.

Back to the Bench:

I removed the Ultrathrust muffler and installed my OLD Jtec manifold with dual pipes. The result was a loss of 400 rpm and lower head temp. I also found that the McCoy 4 stroke plug seems to improve low-end performance. Max rpm with APC 14x4w is now 12,100

Flight Report #2:

Success! Maiden flight went very well. The modified ST G90 performed flawlessly. I was getting 12,100 rpm with a APC 14x4w which provided truly unlimited vertical. Most flying was done at 1/2 to 3/4 throttle. KE flight was extremely neutral. I didn't notice any tendency to pitch in KE flight. Upright flat spin was good but inverted was better. I have not tried 3D yet, however, the modified G90 has great thrust and throttle response. I had to cut the flying session short due to weather conditions. I'll post more as I get more flying time on the Edge.