To my ears, the Distortion has a more modern sound than the Custom. The distortion is grainer, crunchier and slightly more raw. The Custom can be agressive, but is slightly smoother....comparatively. I think the description SD gives the Custom is right on....a PAF on steriods. The Distortion is a different animal.
If I have my facts straight....the DD is a JB with a ceramic magnet. Different coil windings than the JB....maybe even different wire guage. That I'm not sure about.