I don't think the 210AV cabs give a sensitivity rating.
Correct. I wonder, if this is a marketing issue. The cabs, to my ears, are not inefficient. Maybe they don't want to publish the sensitivity to not have too many customers having 4x210AV instead of an 810
The 112AV / 212AVs both also sound great. Maybe (with the horn rolled off) the closest to the 210AV and 810AV, soundwise. I could only test them at reasonable volume, though. Still, the 112AV does sound different, and depending on the budget, going for another pair of 210AVs might be a more suitable option.
Thanks I am a bit concerned about the mismatch. I do remember
@tombowlus review and also
@JimmyM mentioning that max volume between a pair of 210AVs and the 212 were not significant. Maybe I am not remembering that correctly.
EDIT: I strongly doubt, replacing 2x210AV with a 212AV would result in more volume, if that was meant. But I did not measure it, so I refer to Bass Gear:
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"Comparing the double 210AV rig to the 212AV, the two 2x10's are a good bit louder, and definitely more full/warm/round."
Complete online issue with pictures:
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Adding a 212AV or another 2x210AV to your 2x210AV, I doubt, you'd ever have to worry about volume

Since they're in a similar price range, I did try both setups, and went for the sound, not volume. The 212AV may have one advantage and disadvantage, at the same time, in your setup; it sounds different, and can be tweaked with the horn. Since you have but one EQ on the amp for all cabs, this may be cool for getting a new sound - and terrible when trying to keep the previous sound, you liked. That's why I'd try it in the final setup, at the very volume you want to play. Maybe you can borrow a 212AV, and 2x210AV, from your guitar center, to give both a try.
P.S.: Advantage for the 2x210AV: If needed, you can place them apart, or crossfiring or whatever, to overcome room issues.