In my Schroeder Dozer at least the KT150’s came off a little more clinical and distant sounding than the KT88’s, but a little bigger and more efficient/more headroom, but some vintage KT88’s like the Tesla KT88S’s and GEC TT21 KT88’s sounded even bigger than the Tung-Sol KT120’s IME. I’m guessing the difference might be that those specific model wizards are voiced specifically for their respective tubes and transformers for them