Having 7 7 Millimeter rifles and having shot and owned more. I would recommend the 280 AI because it could fill all of your needs without being hard on barrels, less recoil and better brass life. I competed with a 7 rem mag at 1000 yards and it performed great. but was rough on barrels and brass, and had plenty of recoil. and If I were going to build a Dedicated 1000 yard match rifle it would be a 7 STW.
But with all of that said, For an all round cartridge with lots of versatility, good barrel life, case life and 7 mm RM performance, I would build a old style 280 AI that can shoot factory 280 ammo accurately while fire forming to 280 Ackley. It uses a standard bolt face, a 30/06 action and mag, dies are readily available for it and the 280 handles all 7 mm bullets well with proper loading. Its case capacity is suited to lighter bullet loading But can propel the heavies at 7 rem mag velocities and is capable of meeting the larger cases performance with less powder. Loading is straight forward.
Whats not to like.
J E CUSTOM