Hmmm. As a final note, remember that voltage drop is a 'design issue'. The issue would be things such as efficiency (power wasted in the wires) and power quality ( sudden change in voltage caused by other loads being applied to the line).
Efficiency costs money over time, but is not a safety issue.
Power quality is generally an issue with things like how easily motors start, and if lights flicker when other loads are operated.
In your case, you have circuits with well defined, fixed loads. If you have a 277V source, and a _10%_ voltage drop caused by your load, then everything will be fine as long as your loads are happy operating at 250V. You will need to look at the ballasts, and see what sort of taps or supply voltage range they have. It may be that this is an entire non-issue in this particular case.
-Jon
