That large a tank needs less watts per gallon to be low light, and T-5 offers so much light that they do not fit in the watts per gallon guideline anyway.
The better you can spread the lights both lengthwise and back to front the more equal the lighting through the whole tank. 5' is an awkward length.
More fixtures allows you to change the timing on some lights, so you might do this and still get away without using CO2:
6 AM some lights come on, but not all.
Noon-2 PM All the lights are on.
2-8PM some lights on.