I'm a DADGAD dabbler myself, and I use D'Addario PB mediums (56 sixth
string). They seem to go down from standard just fine and will stay there
forever on my Santa Cruz OM. However, I'm planning on swapping out the
Kluson-style vintages tuners to a set of Waverlys. I think having good keys
is as important as the string dimension. DADGAD sounds crummy if the tuning
isn't right on, and if your keys are slipping, then you're in trouble.
I just returned from Zan McLeod's class at Augusta, and I believe he uses
light gauge strings (I don't remember the brand). D'Addarios are cool
because they are consistent, relatively cheap, widely available, and they
come in that neat little plastic package. I always keep a set in my guitar
case; keeps me from breaking a string (based on the fact that you always
break strings when you don't have extras, especially on a gig out in the
country at night).