I too would use the 6500K. While the 10000K will not be better or worse - I like more natural color of 6000K range. Also, from what I heard, the acitinic dies early and is rumored to cause algae. I dont have first hand experience in this but just from what I have read.
How big is your tank? You have to be careful with too much light in a low light tank. IE - for a 55G you will have ~2.36WPG - more than you need. More light means more plants grow which means more chance for problems. Now if it is a 90 or 110XH then you should be fine - I think...
Good luck
Aries