I know a couple people that still reference this thread, and I had some empirical data I thought might help others trying to figure this out. Essentially one of my closest friends has two Surgeon rifles chambered in 6.5 Creedmoor, and he has tried out a 26" barrel as well as a 22" barrel (both with the same contour and rifle setup). He has fired both guns 1,000+ rounds and shot over his Oehler 35P chronograph regularly. It is really a pretty great experiment, and I thought others might like to know what we found.
- 26" Barrel: 2860 fps - This is what he was getting after 1,200 rounds (no suppressor)
- 22" Barrel: 2805 fps - This is what he was getting after 800 rounds (no suppressor)
- 22" Barrel w/ Suppressor: 2833 fps - This is what the was getting after adding a 30P-1 suppressor made by Thunder Beast Arms.
Overall he only lost 55 fps after cutting off 4" of barrel, and after adding a suppressor it cut that to only 27 fps. That is only 2/10 of a mil (2 clicks) at 1,000 yards. He couldn't be more happy with that trade.
I wrote a blog post with more complete details. If anyone is interested, you can check it out here:
http://precisionrifleblog.com/2013/07/16/6-5-creedmoor-barrel-length-and-muzzle-velocity/ 
