Brian Leitz is kicking ass and taking names with a 9 twist 308 in 1000 yard matches.
Just a guess he would kick ass regardless of the twist, and buying a 9 twist is not a substitute for flinging 5 or 10,000 practice rounds downrange. Just saying.
To the OP, a 1:12" 24" which will stabilize 175 SMK's, 185 Bergers and usually 190 SMK's but they are on the edge. A 1:11 certainly will do all of those comfortably and those are nice choices for long range. I tinkered with 155's, but went back to the heavier bullets. 1:11" or 1:10" would be first choice, but I've not seen a difference between those two with those bullet choices.