Ive just got my 600w HPS, and Im using it for one (yes, a little overkill)plant... Lowryder, actually - and its a female - and as you can see from my grow log, Im using it in a cabinet/closet. The space is about 2ftx2ft, and about 5ft high. I have my window open all day and all night, with the fan on a few hours a day in the evening, and the temps range from about 23C to 27C, so all in all its pretty darn good. Im surprised that the temps dont go higher than that, but if they do I can always mount the lamp on the shelf above instead so theres more room
Hope that helps!