Interestingly, Tim deParavicini showed me a cascode ECC88 circuit that got astoundingly high gain, using starved current operation (0.5mA). I didn't believe his performance claims so breadboarded it. And damn, he was right. Gain of 300, at 6V RMS out, H2 = -58dB, no detectable higher order.
Is that something you can put together in a format that will survive shipping to Amir? In the other Carver thread, I mentioned that I have a stash of JAN Sylvania 6DJ8’s that I can contribute. It would interesting to see how a high performance tube product with presumably pretty good tubes will measure.