My advice,
imho forget the marshalls after 1980, take a 70ties jmp marshall, deeper and fatter sounding. Mor mojo.....better working with pedals, quite often they even have an additional plexi charm....
V30 most midrange, you need more volume to get them working (quite harsch highs, beaming speaker, does not get muddy
or
(Pre Rola Greenback) Scumback m75 my favorite, not recommended for high gain metal, deep, cool tasty midrange, great highs
Other 12 inch speakers I like:
JBL 120 DF (not made any more, quite expensive) (clean fender sound or surf, best tubescreamer performance, quite expensive, character, look for original cone)
Blue Bulldog or Scumback alnico (less harsh), best speaker I heard old silver bulldog, best crunch type speaker on earth, works in another midrange
EV (very neutral)
Thats it, try to hear and evalute these, they make a big difference and they are the best in their category , most other 12 inch guitar speakers are only mimicking these originals, imho never better....
Kai