20% will work just fine, like bandeira says it will protect the engine. i use odonnels 20% and i am in the a main every time. unless i crash or break something. 20% will give you a bit less power and more control over the engine. run it at about 220 230 and have good power, you want more power out of it you lean and run it around 250 260 an you have great power. my feelings that 30% and 25% is just too expensive and it creates too much power when you might not need it. i probably wont change because i like the controllable power. i just ran a 2 day event and at the end of 4 out of 5 qualifiers i was tq by 3 seconds over the next guy and he runs 30% all the time. 5th qual was a rocket round this morning and i got smoked cause i broke in the warmup... just run the 20% you will have broader needle settings and your motor will last longer! thats the big thing is making the engine last a long time..