There about a 5-grain difference in powder room between the Creedmoor and the 6.5x55, around 10%, with the .260 in between. This translates to about a 2.5% difference in potential velocity when both the the 6.5 Creedmoor and 6.5x55 are loaded to the same pressures, 75 fps in loads around 3000 fps and less with bullets at lower velocities.
“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.” John Steinbeck
