Ultimately it really depends what you want to do. What type of corals are you planning on keeping, soft corals, SPS, LPS, etc. What you should do it deciede what corals you want to keep then based on your results read up on those corals and coral families to determine care requirements. "Aquarium Corals : Selection, Husbandry, and Natural History"
by Eric H. Borneman is a good book to get you started on that information.
Different coral families as well as individual corals have different care requirements and high or low flow could be the factor that makes a coral thrive or not.
With the above said.... there are alot of opinions about this topic. IMO flow is important to a healthy reef tank, the general consensus is 10x your total water volume, although i had a conversation this weekend at a Boston Reefers Society meeting with Anthony Calfo, author of "Book of Coral Propagation, Volume 1: Reef Gardening for Aquarists" and his recommendation was to have atleast 20x on any reef tank and possibly higher with a SPS dense tank.
Keep in mind there is no "in stone" right or wrong answer most corals with adapt to different lighting and flow conditions.
hope that helps.
-nick
