Yes, I purchased directly from the Detroit Nichia distributor, and got data from their representative. The DS is rated for 30,000 hours, to I believe 70% brightness. The GS is rated for 3,000 hours. This is at spec. current, which is only 20 mA, so overdriving boost circuits can really pull that number down if they are agressive. The CS series was famous for being able to handle a healthy overdrive, and is rated identically to the new DS. Both DS and GS have much lower forward voltages than the older CS's, at 3.2 volts nominal, down from 3.6 volts. That is why Dorcy is getting away with just sticking a DS LED in front of two AAA's in their penlight. While it won't drain the batteries well at all, it runs a long time near the top of the battery, drawing only 28 mA on fresh alkalines, and making decent light on down to a bit below the spec 20 mA level. By the time you get down below 10 mA, most folks would replace the batteries, but it has only just begun it's potential runtime, measured in days, not hours. You can probably see to navigate in pitch dark with that setup for around two weeks straight.
ADD: Here is the Nichia page for 5mm's, but they won't show rated life. It looks like the old CS in white is gone now, replaced by the DS - they were the same price anyway.
http://www.nichia.com/product/led-lamp-phi5.html
Yes, the boost has to be there, you can't get a 5 mm LED up to 15 mA off of one alkaline cell. Nor can you reach 300 mA on 2xAAA direct drive, even Energizer lithiums will only push it to around 80 mA direct, which will really torture the little Nichia.
I am anxious to get to my DMM now, as I'm thinking that I may never have checked this light for draw. That 300 mA number is not very efficient. A Dorcy 1xAAA makes about the same amount of light (with the same LED installed) at about that same current. 2XAAA should be able to push that LED as hard as it should be at not much more than 100 mA. I have the River Rock (Nichia rebrand) 2XAAA "pen" light, and it pulls around 120 mA with an SMJLED-like 5 mm LED, and is brighter. Of course, it is an absolute riot with a Seoul P4 in there, which is not too hard to do - no increase in current draw, either. I love that setup!