Look into the Gast rotary vane pumps. My Gast 0523 is on it's third year in my 1/4 acre pond and I have been happy with it. 600' is a long way to go so use larger line to make that distance then spit out to the smaller diffuser lines. What do you think your system will consist of? (number of diffusers, brand or style of diffusers, depths of diffusers, and such.)

10 psi is about the max of most Gast pumps or at least their recomended max. Mine runs three diffusers and stays pretty close to 5 psi. The trick with these pumps is that you actually get more air flow with less backpressure. A pump rated at 10 psi is more than you probably need so long as your main line is large (maybe 1" diameter). 9 foot deep diffusers will need 4.5 psi, normal line legths can add 1 psi to it, but 600' of line (especailly small line) will add even more pressure requirments...still a ways from 10 psi. Make sure you figure your back pressures before buying a pump or you might get a pump capable of the proper pressure, but not the right CFM

I'm still thinking if done right... a 10 psi pump will do. Let's here about the systems specifics before assuming.

Fish on!,
Noel