I have a Spectrum King SK400+ that I pulled 19 oz of Jack Herer in a 57"x57". I did however have it on a light mover and CO2. I currently use it in a 47"x47" setup. The SK hangs pretty low, so you will lose a bit of headspace in the tent, especially on a light mover. This has been a problem with the more stretchy strains I have grown. The drivers are attached to the unit, so that will add to the heat in the tent. If you are doing hydro, you will need a rez chiller for sure. Also the Current cost is about $700, but you can bust balls at the Hydro store and get it cheaper I'm sure.
I also have a 600 watt Timber Grow light setup that I have over $1300 invested in that I have not (yet) been able to match the production of the Spectrum King, which only draws 440 watts. I will however say that the quality of the bud grown has been top notch. The drivers can be located outside the tent to reduce heat as well.
I will until my dying day, espouse the greatness of Spectrum King lights. My verdict is still out on the Timbers, but they are promising. Overall, I say you cant go wrong with the Spectrum King.