By time your plants get to any size that 4x8 room will be so full you'll have a hard time tending buckets, my room is only 6" shorter and a whole 3' wider and when the plants hit the 2 to 3' size its awfully hard to tend the buckets, I'm back to the wall. My 3x6 footprint is in a poly lined(white side facing inside-black out) 7'x7'6" sealed room with its own functioning skylight & window for ventilation.If it was not for the fact that I wanted room to walk on each side to tend the buckets I would of went 5'x7'6" or the 4'x8' you have. Myself & 2 friends all have similar setups but they are in larger rooms 1 has it lined as I do and 1 does not and when I compare the way my room lights up compared to theirs you can immediately see a difference in not only the brightness but the plants. My plants are much more bushier due to the reflection of the lighting on the walls illuminating the room much more efficiently. We all started the same time with the same strain the same age clones.. only difference is they use GH's 3 part and I use GH's FloraNova, so there is proof that being enclosed will boost the lighting & production but you also need room to tend the system and make the grow easier.....just something to think about.