Discoids and dubia have very similar reproduction and maturing rates. I have noticed the discoid take a little bit longer to mature though.
The big difference for me between the two are the size and shell. Discoid shells are a bit thicker and harder than dubia. I don't feed discoid adults, but do feed nymphs. Whereas I have no problems feeding dubia adults. Discoids are 2.5-3" and dubia around 1.5-2" as adults.