This matches my own experience. In all honestly, low color temperature, incandescent-type light literally puts me to sleep. I don't use it anywhere. 5000K is my general purpose lighting. I might try 6500K where I work to see if it's any better than 5000K. Not sure I would want to do anything under 17000K, but that might be worth a try also.
I'm finding the productivity versus temperature part even more interesting. The most basic finding is higher temperatures lower productivity. This explains why the economies of warm countries are lousy, at least until they can afford air conditioning for most of their work force. Again, it matches my experience perfectly. Summers I pretty much can't do anything remotely productive on account of the heat, even with A/C. The A/C makes a little difference (basically the difference between lying in bed all day versus doing something, even if that something is just watching TV or surfing the Internet). You'll never get me to move to a hot place.
Interesting study.