I don't think they'd perform badly vs what's out there...I just think that you're missing out on an added advantage they they have built in. I'm sure they'll do fine though. When I think you'd notice the most difference would be in the lowest octaves, where the distortion starts creeping up. Having a 6db lower distortion figure could be pretty significant. Though, in the higher frequency ranges, the 2nd and 3rd order distortion would be more easily heard (since we are less sensitive to lower freqencies) so it could matter a fair bit there as well) But, the difference likely won't be huge, and the sub will still sound quite good.
Hmm, 2 things you need to consider, box size and amp. I'd use the descent as the basis, as you don't have the thiele-small parameters to model it out. I'd try to figure out the internal volume of the descent, and make a box equal to about 2/3 of that...and then get an amp that has about 2/3 of the total power of the descent. If you have a 1000w amp, but you'll bottom the drivers with 400w, then you're 1. spending more than you need to on an amp, and 2. putting your drivers in harm's way, as it's much better for an amp to soft clip than to push the driver to XMech and bottom it out. You almost surely will damage the driver if you do that.
No matter what you end up doing...if you want to look for a later project... I just bought a DS12-CV kit from rythmikaudio.com...it should be here monday...I'll post my impressions once it arrives. You have all the parameters you need, plus recommended box sizes, and an included amp that has just the right amount of power.
Not to discourage you from the project...but it's hard to tell what to do without knowing the driver's t/s parameters.
On another, final, note...small variations in box size or amp strength generally won't have a huge impact...so it doesn't need to be precise...just ballpark. (I'd err on the side of having an enclosure that's too large, and an amp that's too weak) You want to be sure that at max output you don't blow things up.
If you want a bigger amp, make a rule that you won't ever turn it up past a certain level. A lower power, higher quality amp is a better bet in my opinion, though. Rythmik also makes non-servo amps that might be just perfect for your design. Their LT circuit on an 350 or 370 amp could do just the trick.
PM me if you want, and I'll start trying to research more about the descent drivers. You may be able to contact ML directly to ask for t/s parameters, though they may not be forthcoming about them.