I have the 5 at home now, and the B7 which I ordered is with the distributor, still to reach me. The valves I have are Hytron for VT52s. Sylvania or Hytron are the preferred choice for 52s. EML 45s for the 45s. For 6A3, i couldn't get a matched pair but a tube dealer said he had a Lafayette and a Tung sol that looked the same construction, so I bought it.
I never heard the 6, but the 7 is supposed to be in another league. It uses DHT (direct heated triode) tech, which is different from previous levels, the DSD is supposed to be the best from reviews, and the PCM was outstanding. I am using a lot of classical and opera to audition, and when I put on Mussorgsky's Pictures, the speed, dynamics, separation, were incredible. Or the way the tuba builds up and decays in the Bydlo track of that CD. Extremely open too. The Big 6 uses the 2A3s, which are more bassy than 45s, but in the B7 you can have them as well as a choice of other valves, so you can play around with the sound for different genre of music.