I'm running a .61 two stroke on my .40 Ultra Stick. I just maidened it this past weekend and loved it. I had to add a bit of weight to the tail and put my battery aft, but it ballanced out just fine. I didn't rip anything off either. You've got to know how to manage the throttle. Anyway, it's your money. Do whatever you want. I can't very well speak on the .60 sized Stick since I've not had any experience with it, but if I were to bet on it, you're not going to have nearly the vertical performance you're expecting. And, if you go with the .40 sized Stick with a .46 sized engine, you're not going to have the vert. performance that way either. So, it's up to you.