Two MP10 seems more practical since you can place one of each end instead of one MP40 on low speed not to create a sandstorm at one end but not enough current to get a good overall flow on the other. The price of 2 MP10 is about not much more than 1 MP40.
Flow is good for SPS but I think you want a more even distributed flow throughout the tank instead of one high flow at an end. That would cause a sandstorm or knock or even rip the flesh off a frag so you can get the same flow on the oppisite end of the tank.