And a fair answer, that addresses the questions. A BackBeat would be less expensive but given those choices, I'd strongly prefer either the BB3's you have now or a BT3 to a BackBeat.
And that adds additional info. I've never played through a Six10 or an Eight10 (would love too, though!

) but, if you want that kind of presence on stage, then I suspect even the BT3 might fall short? But if Alex is aware that you're looking, he would be the right person to help you decide if either is a better enough choice for you to be worth the steep price ($1900 and $2800 USD, yikes!).
I certainly would love to play with a Six10 behind me, but I can't imagine ever playing a gig where I'd need it (based on my personal playing situations, not making any assumptions about yours).