Barrel length is the surprising part.. I cut mine short as a mountain rifle, it's only 24"
The 140's (I used to shoot) before rebarreling had an accuracy node at 3135. That's the highest I took them. Accuracy was excellent, why mess around. I had no pressure nor do I feel I was anyplace near max with them. That barrel shot the 160's at the same speed, but was a slower twist and didn't quite stabilize them. Few hundred rounds later, barrel puked. Put on the new 3c in a tighter twist purposely to switch to 160, and it worked perfect.
I have a 6.5x284 (also with a benchmark barrel) that everyone claims got a lucky barrel that throws (it's) bullets faster than comprehendable. So whether my 264 got a similar "faster than usual" barrel or what, I don't know. I've read stories of similar claims numerous times in the past, and found it very ironic that "I" ended up seeing exactly that (now) in my-own couple barrels. Ain't complaining though! More than happy with what they're doing.