I have a mp40 and a mp10 on a 40g breeder SPS tank. A single MP40 is enough. I had both so I use both, but when I take my MP10 offline to clean, the mp40 can hold its own. There will be dead spots if you have a packed tank, but it moves a lot of water.
Having 2 pointed at each other on random flows does wonders at stirring up everything.