I am running a 7.5 twist on the 6.5 PRC to cover >150gr if needed. Have not tried anything <140gr but this rifle is shooting everything I put in it. I put a new scope on it yesterday and sighted it in with the 143 ELD-X. I already had the dope for the ELD-X and it was a calm morning so it ran it through the range. First shot hits on every plate out 1200yards (500, 750, 1000, 1200). I took a shot at 2000 and saw no dust but didn't drive out to check it. At the end came back to where I sighted in at 300 and added one more to the 1" group already on the target. I don't think you will regret going with a tighter twist. 57.7gr of Retumbo going 3020 and can watch the shot hit the target. I have the ELX-Xs touching the lands and there are no pressure signs. Have not had a chance to hunt with it yet but it is going out for elk and hopefully deer this year. Been really pleased with this setup.