[Dangerous Dan]

you will be fine unless you rip the snott out of the prop, very few contests do a DB check, and if they do you will know ahead of time, if you are too loud you just adjust your atv until you pass. You get an in flight sound score if you don't rip the prop you will get 5's

Actually I have never seen anybody get a sero on sound. So to answer your question IMAC is not that strict, but when you start moving up you will want cans and a quiet prop so you can get 10's instead of 5's on sound.