Depends what you are keeping in it. If just soft coral and LPS, yes it would be sufficient running Reef Crest or Lagoon mode. For SPS I would recommend 2. My 75g SPS tank I am running 2 MP40wES in Reef Crest anti-sync and the flow is amazing.
Definitely not enough for a 75g, unless you like the incredibly loud noise at 100%. It's enough good flow on my 40B now that I took the 90 down to rebuild. I'm still severely disappointed in the value and quality of the MP40, total ripoff in my book.