Generaliztions often don't work very well but noted SPS expert Dana Riddle says that when you think that you have enough flow, double it!! 10x to 20x your tanks volume (flowing indirectly on the corals) is usually the measurment of reasonable flow for SPS. Hi flow is extremely important to sps for 2 main reasons - Food transport and oxygen exchange. A lot of times you will see people with sps corals that are dying from the bottom up. This usually due to it choking from lack of oxygen caused by poor flow and can be corrected. Also, the more water moving by the coral itself, the more food it can capture!!!
As far as lighting, IMO metal halide is a necessity! How much lighting depends on the lay out of the tank. The key is to get a reasonably high PAR (Photosynthetic Available Radiation) value out of your lighting from the top to bottom of the tank (the amount of intense light that penetrates through the water). Metal Halide lighting provides the highest PAR value! This is why people that use VHO & PC lighting have to put their SPS up really high in the tank because they loose intensity the farther they travel through the water. To answer your question, if you had 2 tanks that are 55 gallons but shaped differently, you will need more lighting for the deeper tank than a shallow one! I hope that helps!
