I can definitely hear the difference between some NOS Ken Rad 6V6GT and the RCA smoked black plate 6V6GT I have in my Deluxe Reverb and the same can be said for long vs short plate RCA 12AX7s in V1 and V2 on my Fenders. I have done some extensive tube rolling and have found what appears to be my favorite combos out there for my amps. There is TO ME an unquestionable difference in tone with some tubes. Some are sweeter in breakup. Some DON'T break up. Some are brighter, some are darker. Its subtle sometimes, but they're there. I tend to think they all sound the same for the most part once the whole band gets playing up to volume. The audience certainly can't tell. But I can, and I'M the one playing the amp. That's all that matters.