I've had the OS 91 and the G90, and the G90 wins hands down. In fact, if someone gave me a OS 91, I'd trade it for a G90.
I am not familiar with the Evolution brand, but I have heard good and bad.
BTW, the G90 I had the Slimline Pitts muffler, which was in the WM Midget Mustang.
What are the prices of these 3?
Gary