What if it had a 4A filament instead, and maybe 30% more gm? Let's keep mu the same, or perhaps raise it to 5 or so. R_p would be a bit lower and it would probably have a bit more grid-anode capacitance...oh well, nothing is free.

For me, that's just too expensive a tube to play with. Sovtek 2A3 is maybe 75% of that one, at less than a third the price( and I know that they sound good ).
cheers,
Douglas