I run a 46AX on 5% nitro and it runs just fine with good idle, good transition and no tendency to load up. There are guys at my field who run that engine on 20% nitro. Their engines run fine also. They may get more power -I don't know-, but if so the difference is not obvious. I think it's more important to properly tune your low speed needle than to worry about what percentage of nitro you run.