The 15x6 with a new OS F plug turned 9000 easy today the plane flew worse but vertical semed better. FAR slower and less crisp in everything but vertical for sure. I think the plug might have had something to do with my previous low RPMs - plus the engine has more running now. I'd like to get back to the 15x8 - I'll be trying it tomorrow. I also have a 14x10 APC pattern to try (but I can't use a spinner with that.) I agree - the plane likes to fly fast.