Yoshie, the 6.5 Creedmoor is actually designed to operate at
lower chamber pressures. This was to allow easier case extraction, longer case and barrel life than other cartridges in the 6mm/6.5mm class while still delivering higher velocities demanded by U.S National High-power Match shooters..
The shorter case, ( than .260 Rem. ) allows longer bullets to be seated further out , allowing more powder space, and still function in "short" action firearms.
The .260 when loaded with the same longer bullets, have to be seated further into the case, ( displacing powder ), to function in a short action/ magazine.
In performance there is f*ck-all between them, the Creedmoor uses less powder for similar performance, making it more "efficient". ( slightly )
Where it does make a difference is in "felt" recoil and muzzle blast. As someone who suffers from an acquired brain injury, this is a welcome difference.
Sorry to hi-jack your thread Elmer, getting back to it, nice shooting by any standards.