I will likely be alone, and very dated, in this request. But,
2x15 Dual Showman cab with JBL E130's
There are probably better cabs. My underlying desire is for a smoother, more rounded
-- but punchy (105spl) JBL sound to add more Treble definition and solid Bass
to the very vocal, but easily-buried, G12H and G12M 55 HZ pulsonic-coned greenbacks.
I know the world has moved on. And, this is truly a quixotic request.
The big ported cab, ceramic instead of alnico, 15's instead of 12's
-- are all about rounding out and smoothing the JBL sound.
A Theile cab may make more sense.
I simply had an amazing sound, once, with a 2x12 Celestions in a Bassman cab
and 2x15 JBL E130's in a showman cab.
It could simply be a faulty sentimental memory.
I remember these two cabs together
as a very vocal, expressive and intensely present tone -- unusually so
when used with my Marshall.
Obviously, 2 together in the same amp
is not the same as each one done individually
and then added together.
The merged impedance curve may have been as important
as anything else.
I know this is dated and personal.
But, those are the specifics and that is the underlying concept.
It is very much a 60's thing -- ancient history.
But, 2x15 JBL E130's in a showman cab
might add some unique tone and dynamics to another more expressive speaker.