Thanks Erik, I think your right about the OS. The YS on a pipe is high rev small blade pattern engine. I think I'll go with the OS.
I'm "Intermeadiate (ish)" 3D pilot, I've tried profiles beofre (like the Extreme) and didn't make much progress. I've been flying UCDs (5 so far) with YS110s, and I seem to be able to handle that better. That's why I picked the Primo, for the longer fuse. I probably should just get a good mentor, but few profile guys around here.
Thanks again.