If you are playing through 4x12s with a SS power amp, you need the right speakers. They only sound completely "plexi" with pre-Rola Celestions (the reissues are also really good), and you have 4 choices between the voice coil "weight" and the resonant bass frequency. My personal preference is for the G12H 75Hz, which is kind of oddball. I somehow got given a late '60s (not Marshall) cab with those speakers in it in about 1995 (didn't want it with an amp purchase, but a friend was collecting, and was persuaded to take it to me for free). I then used that cab for the next 10 years+ of gigging without realising it sounded completely magical, and sold it...
Fortunately the Axe FX III and a pair of half decent headphones allows us to scroll through the G12s in H, M, 55Hz and 75 Hz IR versions - mine are supplemented by ML Sound Labs IRs because I particularly like them, but pretty sure there are some of each in the Factory cabs nowadays. The G12H 75Hz IRs sound like my old cab, and I love them for it.
My 2 main gigging amps in the pre-Fractal tube world were a metal face '77 JMP 50 watt #1987 converted to '68 (ish) plexi specification, and a '80 JMP 100 watt 2203 Master Volume. I still have both, but I don't have that cab anymore, in fact only have a '79 Marshall 1960A cab with G12T 75 watt speakers in it. Great sounding, but all bottom and top (kind of Fender'ish to my ears), and lacks the warm low mids of some of the older cabs I enjoyed and foolishly sold. (Owning lots of 4x12 cabs and 2x12 combos is not conducive to a happy marriage when living in a fairly small house.
As far as the amps are concerned, they all sound good to me since Cygnus was rolled out, and only got better. I used to be really selective about the models (and if I remember right there is a Plexi 2203 in there? Honestly, no such amp ever left the factory, but more than a few people made equivalents by modification). Plexi 100 Jump would be my starting point, keep channel 1 up, channel 2 down lower, and neither ever above the 1/2 way point. I like the Presence control way up, it makes the amps even more open as it limits the negative feedback circuit interaction. Plexi 6CA7 is also a "go to" for me. JCM800 2203 sounds like a 2203, and it's not a Plexi, but it's pretty amazing. The model is very close to the real amp nowadays, which is good if you know how to use one, but can be a bit brutal sounding while you are getting it figured out.
Then play with IRs, and you'll wish you had some of those old Celestion speakers in your 4x12s! At least 75% of the Plexi magic was in the speaker cabs in my humble opinion.
Most of all, if you're not sure if it sounds as good as it can, turn it up a bit. It's what Marshalls were made for!