From experience, you're not going to be giving those HDC's much of a work out with 1,125 a piece, you'd be better off putting 2500 on ONE HDC.Looking into the 18" models of all of these. I'm attracted to the BL and the Q because of being U.S. made, but at the same time the CF on the HDC3 looks awesome and I've heard a lot of good about them. I'd be pushing 2500w to a pair so roughly 1,250w to each. Trying to stay around $600 for the pair. For summer I plan on doing a loud daily that can get low, but dropping down into the lows isn't my main priority. I'm thinking of tuning it to roughly 30Hz.
Basically, which of these would be my best option? Depending on if I decide to remove the back seats or not, I would have 12 cubes net to work with, or 14 cubes if I take out the seats.
I am speaking from the perspective of owning an older HDC with the 3 spider suspension, they recently made it two spiders, so it might take less to get them moving now that the suspension isn't rock hard.