They both have their benefits but here's my breakdown:
Mp10 has good flow options and programmability. Sits on the outside of your tank but no cords inside or heat. I'd keep that in mind. Wet sides do wear out but easy to work with.
Gyre, inside the tank both heat and cord. Gyre tends to wear out rotors from what I hear. I've never personally owed a gyre and I probably won't because I'm a MP guy.
With that said. In a 40 cube with lots of live rock I think the gyre would give you better flow. Personally I think two mp10's would be ideal.
This comparison is very subjective. My preference would be the MP10 mostly because you can place it just about anyplace you want, and it seems to create more random flow patterns.
However, if someone like the Gyre, I wouldn't call them wrong.