I own and handload both
My .270 WSM is a 1885 Winchester (Miroku manufactured) with a 28 inch factory barrel. I have focused on the 140 and 150 gr bullets because I own two 6.5 WSMs. The 140 gr Accubond in .277 has a BC of .498. It can be driven to 3280 easily by MagPro and be half a grain less than the published maxium. The drop on this combination is 5 inches less than the 6.5 WSM at 400 yards.
The 6.5 WSM with a 9 inch twist and 26 inch barrel can shoot 130 gr Accubonds at 3280 fps with Retumbo or Ramshot Magnum. The 130 Accubond has a lower BC than the 140 .277 AB so it retains less energy and drops more.
I have just built an 8 twist 28 inch barrel 6.5 WSM but the barrel is being nitrocarburized. I will shoot high BC target bullets with it and not bonded hunting bullets. I plan to investigate VV N-570 powder with those heavy for caliber140 and 142 gr bullets .
Note the 150 gr .277 Ballistic Tip has the same .498 BC as the .277 140 gr AB.
I have tried Win 780, Reloader 25, Ramshot Magnum, VV N-560, 4000MR, Superperformance, IMR 7828SC with bullets in both cartridges. I have tried Reloader 22 extensively in the 6.5 WSM and Retumbo and Magnum offer more velocity with 130 gr bullets.
I have not tried H-1000 in either cartridge although I have experience with it in the .264 Win Magnum and 7mm Remington Magnum. It never showed acceptable accuracy for me and other, particularly double base powers showed more velocity.
I will continue to load both the 6.5 WSM in 2 rifles and at least the one .270 WSM which shoots too well to walk away from. 5 inches less drop in hunting situations from the .270 WSM at 400 yards. Recoil is similar. Barrele life favors the .270 WSM probably but not many rounds. I shoot only HBN coated bullets and all new barrels will be nitrocarburized to extend their life. The first from a clean barrel HBN coated bullet will go precisely to the center of the group which follows. Tell me where the fowling shot from your barrels land and how that impacts your hunting.