RE: Studies...
I found this interesting.
http://www.reeflightinginfo.arvixe.com/select2lamp.php
In the case of 250W bulbs, I noticed that the SE bulb produced more par than the DE bulb given ALL ELSE EQUAL.
In other words, when you: pick the same wattage for both sides (250W) and pick the same ballast for both sides, and pick the same K rating on both sides, and then pick SE on one side and DE on the other side, you'll see that the SE bulb produced more par. This was the case for 14 random configurations that I checked out last year using the above link. (NOTE, don't forget to pick 'N' for the shielded drop down box for the SE bulb)
Here's another interesting research article.
http://www.advancedaquarist.com/issu...04/reviewb.htm
"Comparing the data here and other 250W DE articles with the data for 250W Mogul lamps, should provide enough factual information to dispel the myth that 250W DE lamps produce more light output than the 250W single ended mogul lamps. A general sweeping statement to this effect cannot be made, and depends on the lamp under consideration."
I haven't looked at 250W DE vs 400W SE comparisons but I'm sure someone else can.