I would have to ask, how much extra is it going to cost to get a tube with both sides matched? In theory, it would be nice to have the exact same gain in both channels. But from a practical point of view, what's the worst that can happen if they are off by a little bit, you would have to tweak the balance control a little bit to one side or the other? Most of us should probably be doing that anyway to compensate for acoustic differences in the two sides of our rooms.