Grow tent size question

I currently use a closet, approximately 3x3x6. I use 1x 600w, and that size is perfect, but venting the closet and keeping it cool has been a struggle. I am looking into a grow tent, and am considering getting the 56x56x78. Thats a good 1'8" to both length and width.

My question regards light efficiency. Would my 600w still be sufficient for a small grow, or does the extra square footage degrade the quality of light even if it is the same number of plants as in my 3x3x6 closet. The tent has the reflective mylar lined inside, will that make a difference in light dispersal?

Would you suggest holding off on a larger grow tent till i can get sufficient light to fill it, or can i still keep my smaller grows for now and leave portions of the tent unused? will my babies suffer for it?

as long as you keep the plants centered under the light and you keep the light as close to the plant tops as you can there should be very little difference. a slightly greater percentage of the light the plants use will be reflected @ about 80% efficiency, but probably not enough to matter.

Thanks for the quick reply. I was hoping it wouldnt make too much of a difference. The temp control has given me the most problems, there isnt a fresh source of air within 20 ft of the closet.