I don't profess to be an expert, but here are some reported observations: 5000K-10000K grow plants just fine. Different manufacturers of same kelvin temp will look different due to the coating on the bulbs and what color peaks they've chosen. I've used 5000k bulbs of different manufacturers that have subtle yet noticeable differences in color (all are yellower in cast than 6500-10000k). Scott Hieber of APD fame, favors 10000K as it gives a very crisp, white light, which is what he's after. If you have 2 rows for bulbs a combo of 6700K and 10000k would yield better results than going with just one color temp of bulb, this is what the "experts" say. I have a friend who uses NO fluorescents where he combines Grolite WS 8500K(?) with one at 5500K and looks great to me. On his larger tanks there are 4 bulbs, same combination.

Bill