Erik, I'm really crazy about my Brison 5.8 in my 36# Ziroli Corsair. It has a real solid air frame and I don't find the vibration objectionable at all. The transition is excellent as is the starting. I'm running a Menz standard 26 x 10. It should work fine in your 33% Great Planes Extra although you might notice vibration more because of the lighter air frame. It's really good in "Big Iron".

Ken