Plinko, Short version - I ended up using some NOS short grey plate EI's I had on hand in combination with some Svetlana's of which I have a "lifetime supply" (so it seems). Very full and dynamic yet retaining smoothness and clean clear mids and highs. An excellent combo.
I also tried current production EH's (the best next to the NOS EI's). The new EI's - very clean clear mids and highs but a bit lacking in the bass which made them seem a bit bright (but I love them in 2 of my DAC's and another pre-amp), JJ's which were too full in the bass and not as smooth in the highs, and some Sovtek LPS with which I just made no connection (but these were 4 years old, I don't know about the latest production which I have heard is quite good. I also tried some NOS Chinese very low noise tubes which were too rolled off with the Svets, but which I want to try some time with NOS EI EL34's and E34L's I have on hand. I think that has potential for a good combo.
As it is right now I'm running NOS EI12AX7's, NOS EI12AU7's and Svetlana's.
Can't comment much on the Mullards in your amp but I would probably think twice before i would invest money in seriously expensive NOS tubes until you have a fix on the tonal quality you need in your unit, which could also depend on the power tubes you end up with. Personally, I'd be concerned that the Mullard might be a bit too warm for either of our amps.
Have you or are you going to fiddle around with power tubes? I'm not a big KT88 fan (only from experience in three different amps I have) and admit I'm a bit curious to hear the PL2 with 6550's (like Svet's (SED's) which I use in my main amps. Let us know how your tube experiments go.