So .. some things to balance. The higher BC bullets are likely to be heavier, lower velocity, so expansion can be iffy / ricochet potential goes up. And yet, they have characteristics you need. I think the answer is to find balance, not to maximize anything. My personal choices would be 75 grain VMAX, 87 grain VMAX, and 80 grain Ballistic tip. I would also consider the 85 grain speer boat tail soft point, the new 90 grain ELD-X, and maybe even the 70 grain ballistic tip.
.22-250 with a fast twist .. kinda the same issues, you get out of true varmint bullets with real thin jackets when you start going up in bullet weight. 60 grain VMAX and Ballistic Tip are pretty much king of the hill for reliable varmint performance. A good buddy of mine built a .22-250 AI with a 1-9" twist as one of his projects in gunsmith school. He went out and shot a bunch of rock chucks with it, 500 yards, 600 yards more or less. He was using the 75 grain AMAX. Results varied a lot. Sometimes it blew chunks of rock chuck all over the landscape and other times it penciled through leaving them to run off leaving a blood trail. I think the 1-8" twist is a good thing for targets, paper or steel, and high BC bullets, but it doesn't add anything over a 1-12" twist for varminting use.
What you should do is look at the on-paper BCs of the bullets you're considering in both diameters, look at the velocities each cartridge will push them to, then see which holds enough velocity for violent expansion the furthest. I don't know which it will be. My gut feeling is it's going to be the .243 ..
