Adam,
Every bulb (SE or DE) will have different characteristics (some more than others) depending on their design and method of manufacture. Even 3 different 250W SE bulbs, all rated at 10K, will have a different output. Do a search for "metal halide bulb comparison" and you'll what I mean in color alone. And then theres the PAR, the actual measure of light output. This will be different from bulb to bulb as well.
Acrylic, each 400W bulb will use about 55KWH more per month than a 250W.