I can't answer your targetshooting tech questions because I just dabble in that for fun only. As far as spine I think you need the proper flex in the shaft. Overspined I guess is better then under but there is the perfect balance. The perfect balance shaft to me ex sorbes (sp?)the bows energy while the over spined shaft gives it back. I seen a cool video of slow motion over and under sipined arrows that was a real eye opener. I'm going to try and find it. I seen it several years ago.