RE: O' Donnell 20% fuel
For a beginner and if your not racing, I would personally use the RTR stuff. The reason being if you over lean it the extra oil will help in not totally destroying your engine, now as stated before if you run your engine lean it will hurt the engine no matter what. But the RTR will be more forgiving as it offers more oil, so there will be less damage done.
But this is if you run lean, if you keep the engine on the rich side and keep it going like that then yeah go with the race blend. Just make sure your on the rich side of things all the time and your will be good.