Actually i have the exact same tank. 70 gal oceanic with a center overflow. I also run a sunlight supply maristar with 2 250w MH and 2 39w atinics. I personally have no problems with heat at all. My tank stay in the 79 - 81 range all day with only a small fan running on the surface. I do have a 1/10 chiller but that is more for precautionary measure more than anything else. Personally i light my setup and dont think its too deep. I've actually accidentally bleached a coral or two because I had too much light and I moved them up to quickly.