Very interesting. I do think a 5 shot group tells more about the rifle than a 3 shot, and as often my 3rd shot is the flyer not 2nd, 4th or 5th. Also, the way the rules are set up, barrel heat should be a non issue, there is no time limit for the shots on the target, a fellow could take all day to shoot 1 target if he wanted, shooting either another arm or other targets between shots on a target. In fact, one could concieveably shoot at 5 targets at once, rotating the target fired and allowing for 20 minutes between shots and choosing the best of the bunch. One could do this several times, shooting as many as 50 targets if one wanted, just simply to increase the odds of seeing a really great group.
I don't think 3 shots or 5 will draw or keep participants away. I think people participate for reasons other than winning, after all, what is to win??? This match strikes me as much more a show of personal achievement than a true match where there is actually something to claim.