It's not quite that simple, and acceptable turnover rates vary depending on (i) what corals you plan to keep, and (ii) your specific tank set-up.
I guess a general rule of thumb (and as with all general rules, take it with a grain of salt) is that for SPS tanks, you want somewhere around 20X turnover. So in a 100 Gallon tank, you want about 2,000 gallons per hour turnover from your power heads etc.
For softies / LPS, you probably want around 10X turnover, as they do not need quite the same agitation from flow as the SPS corals require. I guess low flow would be somewhere around 5X turnover, but it depends on what you keep - meaning for an SPS tank, 10X might be considered "low SPS flow". At some point (lets just say 5X and less) there is not enough flow to properly facilitate the oxygen transfer at the surface, so personally I would shoot for am minimum of 10X egardless of what you keep (unless of course it is sea-horses or something like that, in which case you need really low flows).
However, whatever your actual turnover rate, in your tank there will be high flow areas, medium flow and low flow areas. I have about 10X turnover, but I have high flow areas in the middle of my tank (where I generally place Zoanthids), medium and low flow areas at the sides (where I generally place LPS corals). So although I have a "medium flow tank", some areas are very high flow (where the powerhead flows meet), and some areas are low flow.
HTH
Stewart