For me in my area paying about $.114 per KWH my break even point is around 2.5 years. The point where the extra power costs of running the T5s would have paid for the LEDs. Everyday after that I'm saving money.
LEDs are newish so bulb life is not as set in stone as T5s are, but 10-15 years running 12 hours a day is the best guess I could find. During this time period they should have lost about 30% of there brightness. At that point you would pretty much have to replace everything expect the heatsinks as I would guess the newer stuff would not work with the older stuff. Newer stuff so more risk.
T5 bulbs run 2-3 years? Losing about 50% of there brightness over that time. Depending on ballasts and bulbs, there is a lot of varation here.
Page 11 of this thread I wrote a lot about it. http://www.terraforums.com/forums/sh...ing-101/page11
If you need an odd sized heatsink, I've ordered from http://www.heatsinkusa.com/ and plan to again probably in 2015.
I like the idea of removeable and hence replaceable lamps. The non-solder plug in connectors as well. The find your own fixture, heatsink, and/or hood less so. I wonder if a premade fixture with lots of .5 watt lights would give more or less the same light as fewer three watt as in the kit setup. You also have the advantage of tucking away your "plug ins" in the fixture. And choosing your lamp colors. I think for now I would probably fare better with a premade lamp. Nice that you have the skillset and knowledge to set things up precisely for your application and area.