The Sherpa will be 6mm bigger in the same size so it's hard to say. You really want to go get them shell checked to know for sure. Being half a size differnt also means it's not as easy as just going up or down. It's a slightly higher volume so you may find the 25.5 works but go check. You know it's not a din boot though right and it does not have tech inserts for some reason so you will be a little limited binding wise.