Yes it is rough, i have a 30x30x24 and i have one pump front bottoms left one top back right and one on the front left pushing diagniol. I feel its OK. Cube is the way to go though
I have a 30wide x 30deep x 27tall. I have 2 mp40's and my return for flow. My rockwork is open, I have one mp40 on the back center bottom and one on the back left top and my return is on the top right. I can't create the wave effect in my tank but i do have a lot of random flow so its good. My sps seem very happy.
A Vortech or two would give you a very wide flow, yet gentle flow. If you get MP40s, can you easily dial them down to what you need, and, if you upgrade in the future, you already have nice pumps for movement.
i think vortechs can kick butt on any tank. I had just one on my 48x24x20 so i think in a cube it would be even easier. with just say an mp40 i know they push some massive water in a tank. I know a guy who has a 150 with 4 mp10s accross his back and he tank is growing beautifully.