Advice on Powerhead Flow

[gwncpa]

I am putting together a 90 gallon system that will have all soft corals. The only flow right now would be the return from the sump. I am thinking of adding a couple of powerheads. Everything seems to be rated by gallons per hour. What GPH would you use on a 90 gallon? Choices 240, 425 600 or 850.

 

[Dre59]

What's your spending limit? Do you want to place these on the side of the tank or the back wall?