Just tried something which (inexplicably) I hadn't previously, which is to plug my Mesa 5:25 into the 10" Ace 25 (Celestion Alnico Blue-a-like) which is normally hooked up to my Ampmaker SE5a kit build...
It's bloody lovely.
The Mesa's a nice sounding amp and plenty versatile but it's normally quite dark sounding by nature needing the treble up quite hard to get Fendery sparkle out of the clean channel. Plugged into the Tayden Ace it sounds like a completely different amp - I don't know what a vintage AC30 with original blues actually sounds like when you're in the room with it because I've never had a chance to play with one (which is probably just as well for my hearing), but both the Clean and Blues modes of the Mesa sound an awful lot like what was in my head as classic Vox clean, just breaking up, or crunchy tones.
i'm obsessed with speakers. it's an easy, reversible and relatively cheap way to completely change your sound, and if you buy used you can always sell them on if you don't like 'em. The downside is that swapping them about is a bit of a pain and they are hard to store.
If you find a speaker that sounds good, hold on to it! I've bought and sold so many speakers now and the only ones I regret selling are two out of the five Celestion Blues that have passed through my hands in the last few years. This pair just sounded better than the others, kinda wish I'd subbed them out of the amp they were in before I sold it...