No time to write a book :^) but here's some simple considerations:
The 45 is much more linear than a 6J5, so even if the 6J5 is run at half its available peak output voltage (6dB eadroom) the distortion will be comparable with a resistor load. You may get lucky and see cancellation of even harmonics but then the odd ones will be doubled.
With a high impedance load the driver distortion will be much less than the output tube.
If you do not want any solid state, then a choke load on the driver allows greater headroom and high load impedance at the same time. More inductance sounds better, but I have never heard a choke that sounds quite as good as a C4S. YMMV!