Seio Super Flow pump

[CrazyFish]

I was thinking in picking up 2 of theses pumps, for water movment in my tank. I have a 6 foot tank, I would like to put one on each end. Theres a few different models. 620, 820, 1100,1500. Has anyone tried theses powerhead pumps? If so what do you reconmend. If each one would move about 3 feet would be great. I just dont want to buy one thats to powerfull or not enough. I would like not to sent my coral flying. Thanks