I'm not sure how much topology difference there is between the 60 and 75, but I switched amps a while back (still using the red bases.) That being the case, take my opinion with a healthy dose of salt. I have read lots of praise for the NOS Sylvanias and aim to snag a pair of them to try in my new(er) toy, but no practical experience with any NOS goodies beyond the reds in your amp.
The description of the reds you provided sounds plausible, but since I didn't do a side-by-side with anything other than the factory 6H8C and some standby EH 6sn7s, I don't really have a frame of reference. FWIW, to my ear, the reds are definitely a warm and articulate tube in my 75. Verrry sweet.
The description of the reds you provided sounds plausible, but since I didn't do a side-by-side with anything other than the factory 6H8C and some standby EH 6sn7s, I don't really have a frame of reference. FWIW, to my ear, the reds are definitely a warm and articulate tube in my 75. Verrry sweet.