I've had Ei Elite 12AX7E's in the Cornet for about 30 hours and they sound great. These present a big soundstage, an articulate midrange, and a big, authoritative (but maybe a little loose?) bass. They rock hard. I'm hoping their representation of string tone does warm up a bit, though*.
With that success, I ordered an NOS RCA 5814A for the 12AU7, a Mazda NOS Mazda 5Y3GB, and matched pair of Tung-Sol 12AX7s from kcanostubes.com.
Odd thing, when I first installed them, the balance was off about 3 dB. I swapped the order of the Ei 12AX7 tubes and the channel difference came down under 1 dB. Or maybe it was just reseating the tubes?
* Now at the 50 hour mark, it seems to have warmed up quite a bit. I also should have mentioned that the Ei tubes are much quieter than the stock Sovteks.