What 6SN7 for BAT VK-60

You are ignoring the fact also that tubes from different manufacturers of this tube sound different as do they over the period during which they were manufactured. For my old Supertek Syrah, at one time I had 12 different tubes with some clearlly sounding better, not that I recall which anymore. This is the joy and terror of tube rolling.

And very expensive. Furthermore you can also do solidstate equipment. I wonder if anyone has ever transistor rolled.