I ran two Mars II 400s in a 4x8 tent for a year. It performed great when the plants were smaller and i could press the lights. As the plants grew larger and wider, I had to raise the lights to increase the coverage footprint. Veg growth rates slowed a little bit, but by then I was ready to flower them.
If you are open to diy, I have a suggestion for a 5x5 area. post to follow...