I tend to agree with phatsesh that trimming low branches is good in tight quarters. It increases air flow and concentrates energy on prime top buds. If you choose to go this route, only take the TINY, WEAK, SCRUFFY shit that is obviously getting no light. Don't touch ANY of the tops. That messes up hormone distribution in the plant.
Extra 250 MH would have been GREAT at the start of flower to help prevent a lot of stretch. It's fine now too if you can control temps.
Lots of air flow is KEY in a small space, remember! Keep all 6 and add ventilation if you need to.