i was wondering if anyone could give me thier opinion. The 400w i wanted is out of stock at the moment (good price!). But the 600 is a little bit more and i am keen to get started, this will be my first grow in an attic - as i live in the northern hemisphere i plan to grow enough year round so that i can give summer a miss because of temperature control. Anyway the question is how much hotter is the 600 than the 400 the space will be about 4 1/2' *3*3 (growing for personal only) ? thanks