TT2,
I've only flown Norvel BB .25 in combat, but agree with all your observations and those of Ten Man. This year and next I am not flying Open B so I am only using them in scale.

At the Nats this past year I saw a new reasonably priced engine that appeared to outperform all the others. It is a Webra .25. The one I saw was turning a MA 9X4 at 20K on 15% fuel. When the owner told me he was getting this kind of power I blew it off as exaggeration but when pitting with him at the Nats I saw it. He got his from www.flyingzhobbies.com for about $85.

The folks who are running Magnums successfully have worked on the crank timing to bring them into the right timing range to match the rpms we want to run. Lee Liddle won the US Nationals with a Magnum .28, but it wasn't stock and it was running on a pressure bladder so you can't compare his results to what you will get with an out of the box Magnum.

If you want extreme reliability, and not have to worry about your engine so you can concentrate on your flying Ten Man has given the best advise. Buy OS .25FXs and put Kentucky Mousse cans on them (also available from Flying Z) and you will have your power plant issues completely resolved.