Tubes and GAIN on Cary Rom-808

The NOS Black plate 12BZ7 tubes and the 12AX7 tubes are possibilities for GAIN portion of my Rocket 88.

I have little understanding of these. I have them both. I check the bias when I roll them.

Does anyone have knowledge enough to expound on the subtle differences/changes that can be listened for when choosing either one… if there is any?

thanks,Moose