When going up in nitro there are usually diminishing returns. To go to 30% from 20% will not gain the difference that changing from 10% to 20% did.

One other thing you could do is start running the new multi viscosity Cool Power or S&W High Rev Fuel with
New high-performance synthetic oil. The oil is thinner in these fuels and you gain some rpm.

http://www.morganfuel.com/cp_mv.htm Right now it only comes as 15%

There also is a Cool Power 30% Heli with the thinner oil oil....

Keep your fuel in a different jug so they really don't know what you are running? Keep your fuel covered from the sun regardless.