Velodyne DD10 vs DD12

I owned both and the DD12 is what I would call a sub and the DD-10 is like a little boom box! I hope that helps!

Typically larger drivers will go lower in frequency even if only by a couple of hertz with the same manufacturer. I have a Rel B3 with a 10" driver and 200w. I do have 1 song the sub seems to fall apart with and sound flubby. I've had the sub for 4 years and just got the cd a month ago.
If possible try to demo them yourself. If that isn't possible I would say go for the larger more powerful of the 2. You can always tone it down a hair rather than possibly push the smaller one too far.
Just my opinion

The advantage with a small sub is theoretically will go higher in xo frequency. Thus allowing one to intregrate stereo subs better. 2500 sq ft is starting to get a little large for one DD10. Solution : if one is not enough, try two. Just remember, servo does'nt care about Theil Small