I really liked the winged =c= EL34s I had in my first mark V 15ish years ago. Just running 6L6s in the one I just got at the moment though. Sounding really good so I'm not in a rush to experiment.
Out of curiosity... how serious is the manual update about ONLY using variac mode with EL34s? I had my old one before they updated the manual to say this. I never had any issues using regular power mode pretty heavily for the 2 or so years I had the amp. Anecdotally never heard of any issues from anyone else either (and =C= EL34s were a pretty popular pairing with the Mark V at the time as I recall)
This is from the online manual,
NOTE: When using the BIAS SELECT switch on the Rear Panel to accommodate the use of EL34 Power Tubes, ALWAYS switch to VARIAC POWER (switch down) on the main Front Panel POWER switch and operate the amplifier in this power mode until swapping back to 6L6 Power Tubes. This will ensure uninterrupted performance and avoid running the EL34s over their rated safe operating voltage.