I found the track log from ATC that shows his speed, alititude and position.
http://flightaware.com/live/flight/N428DC/history/20090112/0152Z/KSCD/KDTS/tracklog
The plane's alititude and speed stabilized at 3800ft and about 120 to 130 kts respectively (until it crashed) which is what I would guess he jumped at.
I can't imagine anyone doing this without some previous jump experience though. Did anyone find out if he was a USPA member?
One more thing that I noticed is that he landed Sylacauga Municipal and was on the ground for less than 11 minutes which is not enough time to stop and start a turbine so that means he would not have fueled. Maybe he dropped off a passenger that would have picked him up after he jumped?