I would go with the 4x5 and then supplement with 2 t5 8 bulb of the 2ft variety. get the bulbs that are made for the flowering stage and orient them vertically on the 2 longest sides of the garden. this will give the unlit portions of the garden a huge boost and help you to have buds that all mature at the same time. this is assuming that you dont mind coming up with the 300-400 bux for the t5's. I am running a 600hid with a dual spec bulb and a t5 2ft and the undergrowth areas are growing like crazy. there are very few spots that do not get direct light and i try to rotate the plants by hand every day or every other day about 180 degrees. as soon as i can im gonna pick up a 4ft t5. ppl tend to underestimate the power of t5 bulbs.