FLOW!!

How your rock is situated, how big colonies are and how many and how big your powerheads are placed all vary tank to tank.

If your blasting flesh off corals it's too much. If you have cyano and detritus built up you have dead spots. I like LOTS of variable speed flow. I like my flow to be chaotic.
On my 120 I run 4 mp40s on 100% on all different flow patterns throughout the day. I still have 2 small dead spots that I have to stir up with my return pumps loc-line.
I think your going to get a lot of different answers on your question.
I like tons of flow inside display and medium to slow flow in my sumps.

 

A lot. Clearly don't have powerheads pointed at corals so they can't extend - but in my mixed reef that was sps heavy I had 100x turnover from powerheads, that is running them constant, not programs that go up and down, and I would have taken a bit more. For SPS only I would like 150x or more. So I had around 12,000 gph in powerheads. Now I don't suggest just going for the number, you have to consider spacing and not pointing at corals and everything. My range:

1. Softies Only 50-75x
2. LPS only 50-100x
3. SPS only 150x
4. Softies & LPS 75x
5. LPS & SPS 100x
6. Mixed 100x