Hi Rev,
I may be the person Ken is referring to. I can't really help with a comparison between the 410 and the 212 -- I've heard that two 112's don't sound as big as the 212. I do use a couple of UL 112's, often with a UL 410 on larger gigs.
This may be a little "unorthodox," but I'm not a great fan of 410 cabinets in general. 10's just seem to produce more on-stage grunt or bark than I like to hear. I've had 410 cabs from SWR and Eden too, and although the high-end is much sweeter and better-integrated with the Epi cabinet, and the sound is somewhat more refined overall, these cabinets sound more alike than different to me on-stage. The exception, to my ears, is the Acme cabinets, which have much great low-end extension and emphasis, and are, I believe, a little mid-shy.
Having said that, when I couple the 112's with the 410, the combination is pretty full, without as much objectionable bark. Usually, I put the 410 cabinet on the bottom, with 112's closer to ear level. I always get lots of compliments on my sound, particularly from the five or six sound-guys my Seattle-based cover band works with.
These subjective "what I hear" posts are always challenging to write. I've learned over time that they generally tell me more about the poster than about the equipment! This post is no different. After over 40 years of playing and working with virtually hundreds of bass, amp and cabinet combinations, I've decided the only sure thing is that my sound is always GREATLY different from room-to-room, and often from night-to-night! But the challenge of finding the perfect sound is still pretty compelling!
Good luck!
Greg