| The question is, what is the motivation to select the fluorescents.
One advantage of the MH is the lifetime between relamping.
If the fluorescent would be equipped by 2-lamp ballasts, it will have quite significant degree of redundancy, so the overall reliability won't be worse (a failure is only when 4 lamps out of the 6 go dark, what would mean failure of 2 lamps or ballasts at the same time on the same fixture; just one lamp or ballast failure would still mean 4 lamps remain operating, so fixture still working)
The direct energy use is not that different (about 400W for 6xF32T8 vs about 450W of MH400W).
The average light output would be more higher with the fluorescents. If the MH's had very little overlap, the compare would be between MH output close to it's EOL, as that is the worst case and there the fluorescent output would be nearly double.
The fluorescents are way cheaper than the MH's when purchasing the lamps, that will offset the shorter life. That includes even the fixtures (they would have to be replaced anyway and that was the prime motivation to deal with that, I doubt the only reason would be the "energy saving".)
Plus the fluorescent are made in the "very low mercury" form, what means compare to the MH's way less strict rules to handle and disposal of the spent lamps, the disposal cost is way lower. We may know technically it is nonsense, but that is, how the laws are written.
Shorter bulb life with fluorescents will mean more frequent relamping work, the related cost should be taken into account. SO it depend, how much that is (if an equipment to reach the fixtures should be rented for each servicing, it would be way more expensive, so more relevant, compare to when such equipment is readily available there, so it could be used for the relamping with no cost)
But all the above means the maintenance is done right. So the installation is regularly inspected for darkening or failing lamps, the failures fixed without excessive delay (no longer than a week,...). I don't know how it is operated, but this could be an extra expense to count with as well...
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