One of my shooting buddies, uses a 20" barrel 243 for his competitions(usually <800 but have seen him take first at 1000). The "pros" were poking fun of a .243, I think they all ate crow that day. He has built competition rifles,bolt and semi, for 12 years. He was the one that first got me using a 20" setup. I constantly shoot my 20" barreled .308 at 800 and less on steel. While I am not the shot my friend is, I love 20". The loss of velocity was minimal (usually less than 100fps). The twist is more important in my opinion between a 20" and 24" barrel, please know this is just my opinion. I am not doubting anyone, this is just from my experience.