The ESP Guitar Company

Would depend on what kind of speaker was in the amp to begin with, if I had any other speakers to try and how much a new speaker would cost if I had to buy one (celestions are about $100 each new). I bought 4 new Celestion G12T 75's for my old peavey cab at $5 over store cost where a good friend of mine worked and I paid $90 each for them. Most marshalls have celestions in them already, even the combo amps, so I doubt you'd get any "better" tone out of it, just a different tone. But try it...you might like it.

I actually prefer Eminence Over Celestion.

In my experience, V30's have a BIG, warm, midrange, contrasting to the (in my opinion and experience), more trebly and midscooped 75's

+1
dunno about that one. Me and my brother have identical peavey cabs. Mine has the celestion 75s and my brothers has eminence legends and his sounds like crap to my ears. Although I have been hearing good reviews on the texas heats and some of the other new speakers being used by manufacturers in their cabs

Ya, the legends aren't that great. But the TH's and the Blackpowder's, hot damn. And the Lady Luck's are supposed to be great for Blues/rock

Higher wattage speakers won't distort the extreme highs and lows as much. As a result, you get a much clearer tone, but it can often be too clear and sound clangy and harsh. I wouldn't go with anything higher wattage than the 75's. I have a pair of 300w EV-12L's in a cab, and they're like fucking laser cannons.