For what it's worth.
In a review of the Model 11 6.5 Creedmoor the question of the 20" barrel and velocity loss came up. Here are the results of the test."
The 120 grain A-Max ammunition clocked 2725 feet-per-second from the Savage’s short barrel, and the 140 grain A-Max ammo registered an average of 2624 feet per second (fps). This is a loss of only 117 fps for the 120 grain bullet and only 95 fps loss for the 140 grain load, compared to the previously-tested heavy twenty-eight inch barrel. That is not a bad loss at all for eight inches of barrel, and is just barely over 13 fps per inch."
In an American Hunter review, the writer found that the Hornady factory 140gr Amax load averaged 2725fps. This writer also suggested 43gr of Winchester 760 or Hodgdon H100V as ideal for reloading with 140gr bullets.
Apparently the Creedmoor is a very efficient caliber.