The Maxi jets are good (and powerful) units, I had a couple of them going. What I like about my new Koralias is that the flow is wider and more dispersed, which seems to work for my corals which need waterflow, but not the higher more directional flow from a unit like the maxi jet. Since I have corals dispersed around my tank, I need a significant but less focused/directed flow that works the entire tank.
Well, 600 GPH is like 12 x your tank volume, and thats a pretty good turnover ratio. The Koralias are kinda bulky, but the look and the way they mount to your tank is pretty cool/
Cabin, what kind of tank do you have? and what are you looking for in a powerhead?