[Ask around for peoples experience with MH bulbs. The "rated tempature" given to a bulb is often nothing more then advertising. Apparently for example the 50,000K Iwaski (sp) is really only about 14000k.]
[If your already bought two actinics then you might consider using a 6500K or a 10,000K for the MH. Using a 14,000K or a 20,000K in addition to the actinics will be pretty blue. The real question would be what do you want to keep in the tank.]