All I know is the XM 15k is A LOT more blue than the Ushio 14k. They seem more dim also because of the blue. If I were to do it again, Id go back to Ushio 14k, but that is a personal preference.
If you want, Id be willing to sell ya the XMs so I can buy some replacement Ushios. Two for $50. They are about 4 months old.