I've studied this in depth. It is possible for plants to grow under blue light alone but they are not very healthy. It is also possible for plants to grow under only red light, but their growth habit is really stunted. With a lot of red and only a little bit of blue, plants can grow just fine.
Plants grow better under white light than they do under just red + blue. I have absolutely no problem growing under 5000K, they grow great, better than any other special color LED grow lights.
However, I believe that they would grow better still under 5000K white + red. That hasn't been tested.
As for photosynthetic efficiency and wavelength, there are not any peaks, it is a relatively smooth curve. The plant has photosynthetic pigments to be able to transfer other wavelengths to chlorophyll. Theoretically, 660nm and a third as much of 650nm are the best most optimal wavelengths for efficiency, but in reality it doesn't really matter so much. (Those efficiency gains would be trivial compared to other considerations)
Green wavelengths are useful too because they can better and more evenly penetrate to chlorophyll beneath the thin surface layer of the leaf. Which is probably why they grow so good under white light.