Is this lighting ok?

Your post is well intended optimist but the spectrum part isn't quite accurate. Dana Riddle has done tests as to what spectum grows corals the best and even though lower spectrums was once thought to be the only source of growth her article showed that 20,000k actually had SIGNIFICANTLY BETTER growth than 10,000k. I am trying to post the article but when computer freezes on that site(junk computer)
Advanced Aquarist's Online Magazine - Advanced Aquarist's Online Magazine just look under Dana Riddle articles.
T5 is a 5/8th" diameter bulbs T6 then would be a 6/8th" diameter bulb... ALL PCs are T6 but NOT all T6 are PC's. What light do you have on the tank now?
Its a 40 cube you say? Do you know the dimensions off hand?
A single 250w MH pendant or heck even a 150w might cut it, could work on your system.

Happy reefing!

 

you might want to measure your bulbs that are currently in the fixture, before you order and make sure the new bulbs will fit the fixture. this is where I had a problem replacing AT's T6 bulbs with anything other than AT T6's. My 48" fixture bulbs are actually 47.5" and the bulbs I bought at another place are 48"....they won't fit in the fixture.