I always include up to 8000k because in my experience of growing plants indoors for the past decade, that some marginals like the higher color spectrums due to their utilizing algae in the photosynthesis process, much like coral does. That being said, the point is rather moot due to the fact that most people are not going to be running to a specialty (reef shop) for 8000k bulbs.

And as an aside, the lower color spectrums of something like a high pressure sodium bulb (around 3500k) are very beneficial to plants you want to force into flowering. So there are pluses and minuses to all.