Well, I've been through quite a few cabs/speakers (IR/simulated) in the Two Notes library, with the MT15. As one might expect, many cabinets with the same speakers sound somewhat different, probably in part because of their dimensions and specifics of their construction, and then also peculiarities of how the IR's were captured. That being said, there is a large variety of V30 loaded cabs, and for the most part I found them to fall in two categories - Mesa cabs with UK V30's, and other cabs with Chinese V30's, and the tonal difference is very pronounced. Many of the cabs with the Mesa V30's have some massive midrange honk that sometimes can't be dialed out, as the OP stated regarding his Mesa 2x12. With the Chinese V30's, totally different story, they have a frequency spike that very much emphasizes treble-y "crunch" and big bass, but very little actual midrange. The more I play with my own V30's (actual, physical speakers), which are Chinese, and now listen to these IR's, I can definitely hear how my actual speakers line up with the Chinese IR variants. I've been struggling for a while because I just haven't been able to perfectly dial in V30's with the MT15, and I'm thinking to myself "hmm, after all the things I've heard, is this really all the midrange a V30 has?" and I'm starting to think the modern Chinese ones do not in fact have much midrange at all, which explains why, at times, I've gotten dominated by the midrange from the amp of the other guitarist in my band. The Chinese versions have a ton of low and high and a fairly scooped midrange, IMO. Not as much as a G12T-75, but getting there. So I would say the Mesa cabs sound better, at least with the MT15, because at least they have some mids, but it can be very difficult to dial that big honk out. I wonder what cabs and speakers MT himself used to nail down the amp voicing, I know he's a big Mesa fan and I wouldn't be surprised if that's what he used. I won't say the Chinese V30's are necessarily bad, as they sound fantastic with my Custom 50 and obviously I've heard them sound good with other amps too, but I'm starting to question their legendary status as being able to cut through any mix and be an almost universal good match, unless we're talking a Mesa cab. There is one outlier, a Marshall Jubilee cab, which although not being as rich or honky in the mids as the Mesas, doesn't sound as brash either, but it is described as having a UK made V30 as well, perhaps different from the Mesa variant?
On the list of things that didn't do it for me, G12K100, G12T75, Lead 80, and anything Greenback.
There are a couple cabs with G12 H 75-watt Creambacks, and those sounded fair, not perfect but I would say a better match for the MT15. Broader and more adjustable midrange - it came out with higher settings on the amp, but could also be dialed out. Tighter bass. More top end bite too, sometimes difficult to get it to smooth out. A very good speaker for punchy, articulate rhythm sounds, but perhaps not the best for leads, as they can be shrill.
The next one up the ladder, which is somewhat of an oddball, are some Fryette cabs with "P50E" speakers, made by Eminence. These speakers sound, to me, most similar to the OEM Emi drivers in my PRS SE cab - broader mids like the Creambacks, very punchy and controllable bass, and moderate top end bite without being piercing, somewhere between the V30 and Creamback. I believe the P50E's can be purchased direct from Fryette, might be worth looking into as they're probably the best bang for the buck of what I've liked so far, although apparently part of their mojo is being front mounted in all the Fryette cabs that are simulated in the Two Notes library.
Another speaker that landed very high on the list was, believe it or not, the Alnico Cream. Not a cheap speaker, and despite the reputation of Alnico for being a vintage voice, it still took a heavy rock tone quite well. Still had a hint of the alnico mid grind thing going on, but it fit well, and overall a very balanced sound. It was almost like many of the other speakers I've tested were trying to be this speaker, but they fell short and ended up getting weird spikes and hollow spots in their frequency response.
It really is a lot of fun playing with all these cabinets. For those looking for good speakers for the MT15, there are a few options - of course, take with a grain of salt, because I'm just using IR's here. Personally, I would steer clear of the Chinese V30's, the mid cut just isn't there. The Mesa/UK are better, if you want that prominent mid tone to do a lot of talking. Better yet may be a V30/G12H 75 watt Creamback combination (or Emi Governor/Wizard if you want to save a few bucks), those are fairly commonly combined speakers and I think they would compliment each other nicely, each filling in where the other is a little short. Personally, I don't like to mix speakers, because if I'm playing a gig, I don't want to have blend two speaker mics, and even worse if I'm at a show where the house is running sound, I can bet they aren't gonna put more than one mic on my cab, which will result in a very skewed tone. I may try the P50E's in my cab next, and just see how it goes with the rear mounting, or perhaps a pair of Wizards.