Tube Rolling for Rogue Audio Cronus Magnum 2

CMII owner here.  First I tried new Genelex Gold Lion 12AU7's and 12AX7's in all five slots.  A little bit better, but not night and day.  So then I got an Amperex Bugle Boy 12AU7 from Andy Bowman at Vintage Tube Services, and that also is better.  But I'm now still hankering to try a vintage Mullard in the pre-amp position, as stereo5 did.

I also splurged on new Genelex Golden Lion KT-88s to see how they sounded in comparison to the KT-120s, and after a week the 120s are back in the sockets.  More impact, more bass extension, and only very very slightly less sweet.  No reason (now, I discover) to change these.

So, my experience to date: the stock JJ's are not such underachievers as they are sometimes made out to be.  But with some expensive NOS small-signal tubes you can certainly improve and tweak the sound.

It may be aging, or it may not measure well.  Do you know any of history on it?  For $10 more, Upscale sells a specially tested one for CJ and Rogue preamps.

Also, has anybody tried using a Brimar instead of a Mullard on the pre-amp socket?  I keep hearing that they're pretty good, but the Mullard seems tried and tested.