Those are some impressive numbers for 6 month old lights. Looks like the reflectors are a pretty important if not most important component to lighting.
Yea, i read somewhere that if you built a lumenarc and painted it white, it would still out perform a 95% reflective batwing design.
Also, on bulb life, from what i read MH bulbs break in and loose about 25% of output in the first 3 months. But, at the 2 year point this study showed they still had 68% of original output. so from 3 months to 2 years you only loose 7%. As long as you are running >10k bulbs you really dont have to worry about spectral shift (normally shifts to the warm direction)
Where did you get the solar tubes?
Home depot, 20"tall x 14"diameter $45. When you roll it out it is about 20x43. I scaled the lumenarc plans to 20"x20". you get 2 per tube with a little scrap.