Yes, I tried the EAT 12ax7 and KT88 on my (2) MC275 V and never look back. Also purchased 4 extra KT88 going forward, just incase they stop making them.
One friend brought 8 EAT 6922 at the CES last year, that he'll never pull them out.
When I had my Octave I had TS 6550 solid grey and black plates (no holes). I also had SED 6550 and KT88's GL KT88 Russian reissue. Ei KT90's - Eat KT88 diamonds original GEC KT88 and TS KT120's. I would rank them from warmest sounding to most linear this way. TS 6550 black plates (warmest) then grey plates - SED KT88 - GL KT88 - Ei KT90 - Sed 6550 - Eat KT88. The KT120 was kind of an oddball IMO which I did not care for. Punchy lows - glaring mids and highs that sizzled instead of sparkle.
That said a lot depended on which speakers I had. The Dyn C1's sounded great with the warmer tubes and the Raidho D1 and D2's sounded much better with the more linear sounding tubes.
I had little time with the Eat KT88's because I lost 4 of 7 tubes (all purchased used) in less than 2 months. I'm sure I would have liked them the best with Raidho's.