I have many shorties... I worked up loads and tested them before and after bobbing... with a couple, I bobbed from 26" to 18" in 2" increments and tested at each length... what I found was, that my best load at 24" was still my best load at 18"... I gave up 100-150 fps for a 4" bob with identical loads... there was zero loss of accuracy and a few were more accurate after the bob, perhaps due to a better crown... some of the velocity loss can be made up with a stiffer load, however in my attempts the max loads often did not perform as well in the accuracy department and I worked back down to find a consistently accurate load. None of the rifles that I bobbed were chambered in 6.5X55, but I have done .260, 7-08 & 7X57... so I believe my findings would hold true for you also...
My subjective take is that for a hunting gun, the bob rendered a much nicer carry gun, far more wieldy and balanced... I did not regret any of the bobs with one exception... a .308 went completely "to pot" and I ended up scrapping it and starting over.