Thanks everyone for your help and input, much appreciated.
I decided the best set up for my needs is the 11.75" Cordoba factory style "cop duty" disc brake kit. I talked to Dr Diff (Cass) and he's going to price me up a kit today. He said 11.75" is about is big as you can go with 15" rims. He said he'd put together a kit, good price too and more than ample braking for street needs, even mild track. So now I'll be running all Dr-Diff disc brakes, although he said the Cordobas aren't "his", being factory, still, same "supplier".