[mikethedruid]

From my own experience, any well matched set from a reputable manufacturer, whether Mullard, or Philips, or RCA, or Sylvania, will do fine for the push pull output, and that is the only place it makes a heck of a lot of difference, and, of course in the parallel - push pull combinations one needs a 4 match..Of course, in either case, after 6 months of use, the match won't be nearly as close anyway. For the single stages, as long as the tube is within spec it should be fine. More often any distortion problems are more likely due to aging parts whose values have shifted than what brand of tube one uses as long as they are in spec and decent tubes. There was a great deal of silly mythology and audio snobbery back in the tube days driven by manufacturer's hype, just as there is today.