I started the thread on the JBA .56. I also have 2 OS .55AXs and an SK 50.

The JBA does not respond to a Jett tuned muffler like the OS, so I do not think it is set for high rpm that much.

I have it on a Goldberg Wild Stik, but only have 1 flight. I have been under the weather with the bug that's going around. Before the JBA, I had the SK 50. I flew both on an APC 12.25x3.75 3D prop. The JBA gives more vertical. I did fly mostly at half throttle due to the large controls on the Wild Stik and got no loading up. Seems to be a good carb.

The OS is the sweetest running engine, but, as you said, it's pricey. If I was going to pick between getting another JBA or SK, I'd get the JBA 56.