It used to be 3 to 5 watts a gallon like with MH and T5's and such but led's are a little different and I think its more about how much shadowing you have and how it looks to you. What's the length and depth of your tank.
I would go with 3 AI Hydra 52's or Ecotech xr30w pro's both are top of the line. The 52's are 130 watt and the xr30w are 165 watt each and with the depth of your tank your going to want a little higher wattage.
an 8 bulb 80W fixture would be perfect for that tank. or 3 LED fixtures if you wanna go that route. Usually the radions and stuff cover about 2' of tank per fixture??