actually had a friend that did very well with a 6.5/7mmSaum. Smaller case and longer neck worked out better in the Remmy short action without as much case intrusion. If memory serves me correctly.
I'll throw my 2 cents in. The .256 Newton. All the new ai cartridges and wilcats are chasing velocities that you could get with this 6.5 cartridge in the 1920's.
Personally,if your using it for a hunting rifle I would go with a .256 Newton. I use one built on a Rem 700 24"barrel reformed 25-06 brass opened to 6.5. Light recoil,very accurate with 2900 fps with 129gr bullets.