IMO the problem with 20K bulbs (lump in the 14K and most 10Ks) is they completely lack coverage of the red end of the spectrum. They may be pretty to look at, but I personally feel there is a price to be paid for running less than full spectrum lamps.

In the simplest terms, when I look up I see the sun as being yellow/white in color, so my tank lamps are the same, so supplementing them with actinics gives us the dawn/dusk effect and makes up for any defficiency for the shorter wavelengths.