many people use and mp10 in a 30" long tank and still dial it back. i think you should be good to go with a 30 breeder.
you will have to aquascape to allow more flow on the other end of the tank. in 40 breeders, i know people use 2 mp10's, so as things grow out and block more flow, you may have to add another powerhead. 2 koralia 1's will definately not create enough flow for an SPS dominant tank