Yep there seems to be some vert string reported farther out by a few fclass shooters that seems to go away as you get below 8 twist. But I do not recall the vel they were driving them at.
I thought someone might be using a 264WM for 1000 yard benchrest. I saw one years ago at Williamsport in the heavy gun class. I may give it a try. There's no formal competition around here. Hopefully that will change.