Need to talk cabs: Mesa 2x12 vs 4x12, or potentially a Blackstar?

I own both the recto 2x12 horizontal and recto 4x12. They really don't sound that different from each other. The 2x12 has a slightly different depth to the sound. Still similar. I wouldn't say it would make or break a guitar tone.
 
Not sure if your mind is already set on something, but I'm personally very happy with Mesa Roadster 2x12.
It's abit cheaper than Rectifier, but it was Ola's early amp videos that inspired me to buy this cab.
Mesa have also changed it's name to 'Rectifier Compact' for some reason.

Here's a quick snippet (mtallica alert!)

https://dl.dropboxusercontent.com/u/1147572/Tokyurot - Marshall 8100 + Mesa Roadster.wav

-> Duncan Distortion + Maxon OD-808 + Marshall 8100 + Mesa Roadster 2x12 + SM57.
 
It's really difficult to go on this sort of information, because one person's clip of exactly the same chain might not sound as good as someone else's. Totally dependent on chain/room/position in the room etc. All 4 Mesa 2x12 clips I've heard are COMPLETELY different :lol:
 
I've owned 3 Mesa 4x12's, two slants and one straight, all V30, and I've also owned a Mesa 2x12, however, loaded with Greenbacks. (And a couple Orange 4x12's...and a Marshall 1960...)

The 2x12 was tighter in the bottom, even with the Greenbacks. The fucking thing still weighs 70lbs, and is massive for a 2x12. You won't really be missing the punch with it.

Over at Signals Audio we created some IR's with a Mesa 4x12 and 2x12, if you want to have a go with them, PM me.

All anecdotal and not a true comparison, but I really really really liked the 2x12 loaded with Greenbacks. Wish I hadn't sold it.