It will depend on the types of corals you want to keep. The fish won't care regardless.
For Soft corals, 20-30x is just fine. LPS prefer something in the 30-40x range, and for SPS it's nearly impossible to have too much. My 120DT is at about 70-80x, using 4 power heads and a pair of gyre 250's. All are set to different programs and pointed all around the tank so that the flow is as chaotic as possible. If all are at their minimum at the same time, it is almost calm. If they all happen to hit max at the same time, well, ever been caught in moderately heavy surf? It's kinda like that.
More, but smaller power heads that add up to the total you are looking for will always be better than just one because you can them make the flow more random.
HTH!