The SLS design is driven by two imperatives: to achieve particular lift goals (initially 70 MT, later 105 MT and finally 130 MT) and to re-use Space Shuttle and Constellation technology.
Spacex and Elon Musk have the 61 page presentation of the Interplanetary Transport System and the plan from early exploration to a sustainable colony on Mars
However, besides the test firings of the new Raptor engine that is needed for the Mars transport, Spacex has also built a full sized carbon composite fuel tank.
The Interplanetary Transport system can launch 550 tons to low earth orbit which is nearly four times as much as the Saturn V. It would be over four times as powerful as the SLS in the final version of the SLS
SOURCES- NASA, Spacex