We are tube gluttons!!
The 6V6's
are smoother/warmer. I can't recall what else you've run for 6V6 - have you tried the popes - my favorite of that tube so far? The 6550 didn't do it for me but, no vintage Tung-Sol to try - had Tung-Sol reissue and Winged C's.
Another variety to try might be the 6L6 - oh nooooo! More tubes!
BTW, I read somewhere that the solid grey in the Popes and some other 6V6's was for RF shielding - don't know if that's been mentioned here.