Ok guys, I installed the SSTT last night, and I've put about 50 or 60 miles on the car with it on. I'm not feeling any lag at all that wasn't there before.
In first gear the tires have now become a limitation, but otherwise I'm pretty happy with the results. One thing I've noticed is that you have a be a little more carefull when applying power coming out of a turn. The throttle response is a little touchy in certain situations compared to stock. I'm sure after a few days of driving it I'll adapt to it and won't notice it as much.
Something else I've noticed is that now that I'm getting a lot of wheel spin in 1st gear, the car is significantly faster with the traction control/DST completely off, and the eDiff doing it's job. I noticed the touchy throttle response the first time after doing a couple of 1/4 mile runs and nearly got myself into trouble exiting a corner. I turned the nannys back on to give myself a little more time to get used to it.
I'll report back after a few more days with it, but so far I'm pleased with the results. I'm not sure what else you could do to get a gain like this for less money and effort. My neighbor was working on his Mustang while I was installing it and he was annoyed when I told him how much power it was good for. That's just a little less than what he got with a set of decent heads.