Re: 6.5 Rem Mag or 264 Win Mag???
Having worked with these cartridges over the years, and a big fan of the 6.5, I have found the 6.5-284 to be a good balance of velocity, accuracy, barrel life, as well as the easy availability of quality brass. Contrary to the conventional wisdom, the 6.5 -284 is at least equal or better than the magnums as far as barrel life is concerned, shooting conditions being equal. The case design seems to be excellent for achieving very low ES. I get 3025FPS out of both my rifles, 24-26" barrels with near 100% case usage. This velocity seems to be at the high end of the 140 VLD's sweet spot. I can easily get 10 reloadings out of Lapua brass. My intention is not to discourage the use of the magnums, both quality cartridges, but wanted to offer another viewpoint given the OP's stated criteria.
"Let us speak courteously, deal fairly, and keep ourselves armed and ready"-T. Roosevelt