Bring both 210s and stack them vertically behind you, but only use the top one, cut bass, and get and HPF if it's not too late.....
@hasbeen, you should head to the gig and help sound-check!Interesting gig. I helped develop the Neo-X and "voiced" it. That cab is great for cutting through the mix. One thing though- I LOVE low mids. They are a fickle friend though. They really add punch but as well, they can cover up regular mids too, making it difficult to hear yourself. As well, they can add mud too just like lows.
BTW, I live just up the road from the brewery.
I've not owned a 210AV, but I've played through them in a few different rooms. Haven't owned a NeoX 212, either, but have gotten to play through one once or twice (and some of the Genz cabs - the second-gen, 1x12 Shuttle combo in particular - on other occasions - I've more experience with the amps than the cabs).
While I think either setup could work well (as well as can be expected) in a boomy, reverberant room, if I was uncertain, I'd go with the 2x210 stack. You have, as @lomo said, the option of unplugging the bottom cab if you need to (the elevated cab will be closer to your ears and have less boundary reinforcement in the lows and low mids than if it were set on the floor). Too, those 210AVs don't put out a lot of deep lows -- for what it's worth, they've seemed to slot pretty easily into the pub/small bar mixes I've played them in.
An HPF pedal can help clean things up -- sometimes a little, sometimes a great deal. Whether the mud and rumble reside in the deep lows or somewhere in the upper-bass-to-low-mid region seems to depend (at least it has for me) on the room and what else is going on in the mix.
Whether you have PA support or not, keeping the volume at a reasonable level (as a group) can help.
Best advice I can offer you, beyond what's been said, is to show up early if you can, experiment with cab placement (if that's an option -- sometimes the best spot will surprise you) and play with your EQ -- see if you can find the frequencies that boom and take them down a bit -- sometimes even a couple of dB can make a big difference in a mix. (If there's a guitar or keys player, they can help with judicious EQ, too -- bass knob on the guitar amp can be almost fully down and still sound big and clear in the mix.)
Step away from your amp and listen from out in the room (or at least the length of your cable) if you can. A trusted set of ears in the audience can be a help, too.
Good luck!