Like Rex said, in such a large tank the WPG rule doesn't apply too good, 2WPG for such a tank should be good to grow anything. Considering the length of your tank and I believe it has 2 braces, using 3 bulbs would probably provide the best light spread. So 3x175W would be my choice. If using pendants then you could go with 3x250W and simply raise the fixtures if you find the light intensity too strong. I certainly would not be considering 400W bulbs though. I also think that 40% loss is a little exagerated, changing your bulbs every 12-19 months is sufficient IMO. Using more light would most likely just cause you algae issues, plants can be sped up with lots of light and CO2 but not indefinetly, there's a point where more light does nothing good to the plants, you'll just be adding heat and problems to your setup.