The first mission to the ISS by Dragonrider (and CST-100) is expected to be unmanned. That means when it returns, it will have ability to return a full cargo load.
Of course, ISS payloads are often volume not mass limited, and a manned Dragon will not have the proper storage 'shelves' and 'fittings' for payload.
But does the return capacity of Dragon manned (Dragonrider) vs Dragon Cargo differ.
This could be different due to either parachute changes or else SuperDraco landings on land for Dragonrider.