The difference in powder capacity is so low that I don't think you would be able to measure a difference in sound with a proper meter much less your ear. Shortening the barrel by 2" may or may not make much difference either. If you're trying to decide between the 2 cals by sound I don't think it will be an easy decision....they won't be much different.
I have a 21" 6.5x47 and she kicks, even with the 107gr bullets, compared to the 26" barrels that I am used to. Rifle and attached kit weigh in at 13lbs. I attached a Mini-Muscle brake (from Bugholes.com) and that did the job of taming it very nicely. I agree with Biffj - you will not notice any difference between the three cartridges at 20-22", at least any differences that will actually matter to you.
My 21" 6.5x47 moves a 130gr bullet at 2800fps, is a joy to shot with the brake and its light weight/slime profile.
Frank, lower decibels is always nice to my tinnitus, have had a desire to build a 47 since intro'd at the Shot show years back....I may be wrong, but my Creedmoor seems tame in a 24" sporter, it might have a tad less bark than the 260s I have run, just none side by side to compare right now. Blast is one deciding variable, certainly do not like magnums, recall a Mohawk 308 years back being pretty loud. If our state gets ok for hunting, I might invest in a suppressor down the road. Thanks all.