Can't you put T5HO in one side of 8-foot table, and then use your current T12 (maybe 4-6 bulbs) on the other side? You'll get more total light than using spiral CFL bulbs at the ends. Even with 4 feet 4bulb T5HO, you'll need to place them fairly close to the plants (1-2 feet instead of 4+feet as you illustrated in your original post).