What I surmise from the info that you have provided, is that determining high pressure loads is a crap shoot without sophisticated diagnostic test equipment. I checked my data base and found that I had chronographed the 6.5 Creedmoor load in question. Perhaps you can make an educated guess as to what pressure I might be running? Here are the specifics:

Rifle – Savage Target Action, McGowen 28 “ SS Heavy Barrel (Douglas # 9 Contour)
Case – Nosler
Primer – WLR
Bullet – 120 gr Sierra MatchKing HPBT
Powder – IMR 4451: 44.2 grs.
Velocity – 3102 fps

Thanks for the input!