Thanks for continuing to consider more of our products.
Well I think you've laid out all of your needs (and quarks) in your post, quite well.

Of all the choices you mentioned, I'd probably consider the BA12-3 as the best option. My reasons, first the BA210-3 is a much wider cabinet than the little BA10-2 cabs and I don't think you'd be comfortable with that visual. Frankly I'm as anal as you are about size and fit of my rig. I also think the BA210-3 cab might be louder than the others.
Adding a 3rd BA10-2 is always a good way to go but my thought here is --- you already have 2. You're looking for a 3rd cab to really make a presence known on a big outdoor stage. I think that calls for the BA12-3 cab --- either SLT or STR. Actually the STRAIGHT one might be the better choice.
Adding this larger format cab will give you the bigger tonal footprint you're looking to achieve for these bigger events. I think it will be more impressive output wise than 3 of the BA10-2 cabs.
And I think the look will be close enough for your "how's it look" comfort zone.
AND, it also gives you a cabinet to throw a twist into your gig rig options if you care to just take on cab --- the larger BA12-3 for some events.
I hope this gives you some food for thought. Thanks again as always.