8x3 feet Im thinking 2x 4Ft 8 tube T5HOs in a scrog, then your 4 Ft hight wont matter either as you can keep em small in a scrog and keep the T5HOs close, heat wont be much of a problem either
but yea personal preference is what its all about, I bet a few 400W HPS could work as well, but then I would for sure invest in some cool tubes and a good big ventilation as it will get hot in there with out ..
there are many ways to Rome