I don't know if I'd come to that conclusion as gospel. It's gonna depend on how the judges perceive your plane in the air. I'd say if your prop rips on an upline, your under propped. If everyone else is running cans and 3 blades, and your running standard mufflers and a 2 blade and assuming you don't rip the prop at all, you could still receive an ok sound score, which won't get you grounded, while everyone one else could get a quiet score, which will be a penalty to you because of the way the sound score is weighted.

It's all gonna depend on what your comfortable with, what the judges bias is towards it (this is a subjective score), how sensitive the field is you'll be flying at, etc.

Practically all of us that compete regularly are doing everything we can to get our planes as quiet as the current technology will allow us in our region. You should attend a contest in your region, ask questions, and get opinions from the guys you'll be flying with. They'll be glad to talk to you about it.