I have a 58gal + 10gal sump with 400W MH lights. I run the big light from 1pm to 9pm, though I am going to adjust that shorter and later in a few days to compensate for the weather. I have four small computer fans on my MH fixture to evacuate the excess MH heat. They do a great job. I also have two computer case fans on the sides of my tank blowing across the water surface. Typically on an 80-degree day, the tank will not exceed 82 in temperature if I have some windows open for breeze and shades pulled.
If things get worse, I also have a normal floor/desk fan that I turn on and point along the long side of the tank. This moves the air that's trapped between the tank and the exterior wall, which is hotter than the rest of the apartment. This helps significantly.
This last largest fan uses about 40W of power on maximum setting.