Hi, WG. Very interesting, I did not experienced all the “other” KTs but went from EL34s to GL KT77s and they were good from the start, but the sound steadily improved with use, and after a good burn in I have to agree with you: these are simply exceptional tubes. Not only in the standard categories of good bass, mids or highs (which they have) but in their superbly linear and musical presentation .
Difficult to describe, after rolling a lot of pre and driver tubes in the 3502c, (in integrated mode) while in power amp mode doing the same with my nice FA Euforia preamp, (and I mean top notch vintage TFKs and Mullards with this one) the GLs were revealing of every nuance...even from the 12AT7s drivers. That’s why I strongly suggest the Brimars. Fantastic sinergy with the KT77s. But the exotic E180CC...come on baby, pure and unrestricted triode sweetness.