My coralife aqualight is a 2 x 65 watt fixture. THe fixture has 2 ballasts, one for each bulb. Thats all i know about the ballasts.
The bulbs i got were labeled 55/65 watt bulbs: http://www.reefgeek.com/products/cat...ng/103031.html
Right now i have 1 8800k, 55/65 watts bulb plugged in, and 1 6700k 65 watt bulb plugged in. 8800k definitely looks a lot better but having both on brings out the best result, but 2 of them on at the same time is too bright for my aquarium (130 watts over 20 gallons).
The new 8800k bulb is noticeably bright, but that could be due to several factors: new bulb vs 8 month old bulb, different colour sprectrums, etc...