I know you're interested in 2006 figures, but here's some info from my 2007 brochure :
RAM 2500 Mega 8800 GVWR has 2220 lbs payload capacity.
RAM 2500 Mega 9900 GVWR has 1610 lbs payload capacity.
RAM 3500 Mega SRW 10100 GVWR has 2690 lbs payload capacity.
RAM 3500 Mega SRW 10500 GVWR has 2740 lbs payload capacity.
My 3500 SRW handles my 18' car hauler better than the 2500 it replaced; the ride is not sacrificed as the overloads are not contacting unloaded.
The 3500 SRW is the way to go, IMO.
Greg