Well I think the results may be in for this test. I have explosive
growth on the 6500K side of the tank....and the same thing on the 3500K
side. I forgot that two days before I changed the lights I started C02
injection.

So what did I learn? Well if you have adequate light to begin with then
adding C02 is more effective than a 0.6 watt per gallon difference in
light. As evidenced by the fact that both sides of the tank are growing
at the same rate despite the light difference - obviously C02 was more
of a limiting factor for my tank than light. I'm going to leave it the
way it is for at least a week just to be absolutely sure but in the end
I think I'm just going to go with the light that looks better. That
would be the 6500K - I don't think it's any better for the plants, but
it does look more natural. The "soft whites" reflect off of some orange
rocks I have in the tank rather harshly because of their orange
tendancy.

-Daniel