The LEO payloads for FH and SLS block 1 are similar but SLS can put nearly twice as much mass on a trans-lunar injection. There's also the larger faring size o

The LEO payloads for FH and SLS block 1 are similar but SLS can put nearly twice as much mass on a trans-lunar injection. There's also the larger faring size on SLS and future blocks will have more performance. All of which isn't to say that SLS is cost effective, but it does have capabilities which will be unique for at least a window of time.