Does anyone have the specs for a SSD 15 with the high QTS upgrade?  I am looking to use some in a 4th order build and I am trying to model the subs.

4th order vented or band-pass?  It will have really bad ripple in a vented alignment...

Bandpass. Originally had xfl 15s. Looking at going to a more 4th friendly sub. I was almost set on sa's but decided to look for something different. Almost everyone with a 4th goes sa. They are proven, but I think the ssd deserves a shot.

Well good luck!  Just make sure you MODEL first and don't arbitrarily choose volumes and tuning...  The High Qts (and other attributes) allow for extremely small sealed alignments with a low Fc.  It might make designing tough due to a vented section being to small to properly support needed vent area, unless you go external venting...  But again, be sure and model before hand so you know what you are getting!

Build is already complete.  Mike Singer designed and built it for xfls.  Sealed section is only 1.25 cubes sealed per 15.  The xfls worked well just trying to find a more 4th order friendly sub to help with efficiency.  Build did a 160.9 on 15k clamped.  Just trying to see if a more friendly sub will be better.  I want to try and get my power down to around 12k.

Again, modeling will answer your questions once you find specs, especially since you already have the box built!