I have an Ultra Stick 40 with an OS.55 in it using an APC 12-4. It has good climb, but not eye-watering climb.

I tested the .55 on a 12.25-3.75 APC with a Jett tuned muffler. I tached 14,500 on 10% castor blend fuel. With a tuned pipe, I'd figure another 200-300 rpm so make that 800 more than your Tiger. This still won't give you stupid climb.

I used to fly tuned pipes all the time, but finally just went to larger engines. I'd put a .91 in it.