Very true about EL84 v 6L6 !
I've got a Lonestar and a Lonestar Special and with the Special I found the only real improvement was a speaker change if you want to spend the money. I put an Eminence Delta Pro 12 in and use a Creation Audio Labs MK4.23 in the effects loop for power valve boost. The Delta Pro gives stacks of head room at both ends and, I've noticed, currently reasonably priced. Don't be fooled by them not being listed as a guitar speaker, lots use them and I've installed them in my sons Randall, he's well pleased. They simply give you a lot more of your amps tone with minimal colouration and phenomenal projection. Bit of a pig to fit in but is a do-able, Mesa were really helpful about the upgrade which is basically longer mounting bolts and 8 instead of 4, the speakers **** heavy, an easy DIY just go slow.
But you will still be an EL84, although better, and as I've found, changing valve brands only difference, except maybe one, is a hole in your pocket. You just will not get the thump of a 6L6 loaded Lonestar, but that's why there are 2 beasts with distinctly different characters.
Good Luck :mrgreen: