I have seen XTOL's gms 47 run, and his does run pretty nice, but he is our clubs engine guru, so we always expect whatever he has mounted to run good.
For everyone else without the magic touch, or without a touch of luck like me, I found my GMS .40 a little stubborn to tune, so I did what I do to all engines that don't cooperate, I got rid of it! I also got rid of two awful Tower .46 Engines made by GMS for Tower. I have heard of less troubles with the GMS 47 than with the Tower 46, so there performance/quality seems to change among various GMS Engines . I have never owned the GMS 90, so it may in fact be a better engine than the 40 I bought. I just wouldn't want to waste my money finding out, when I do know that the Super Tigre 90 ran pretty good for me, and seemed fairly easy to tune, and keep in tune. Experiences may vary though!