I used to run big cats. Sold them all and went to gas for larger engines.

All my cats had the OS7D carb.

I picked up 300 RPM on the 3000 swinging a 20-6 Zinger on 5% Omega and a Tower plug at 6000' elevation. RPM on the bench was 7200.

One thing I quickly figured out about the OS carb was not to adjust it too rich on the high side. You had to adjust for max lean and then only back down about 2 or 3 clicks. Anything richer on the high side and it would die if you chopped the throttle quickly back to idle.

I couldn't say how the other engines ran after the OS carb was added, I bought them all used and they already had the carb. No way to compare it to stock carb.