How things appear under metal halide light depends a lot on the brand of a lamp and the combination with a ballast. 14K Phoenix appear a lot bluer than 15K XDE (a double ended version of XM bulb). However, after a few months of use, I cannot tell the difference between 20K XDE vs. 14K Phoenix.
You should check out a shop with tanks lit with various lights. Philip helped me out a lot when I went to MH lighting when he was still at Fish Tail. He showed me various light bulbs and ballast combinations in use over several different tanks. Some shop like CRA has a few tanks lit with just MH bulbs using 20K or 14K bulbs.
Tomoko