I would go with what you like. Any of the bulbs are fine for reefs. The 10,000K will have a little more PAR than the actinic for coral growth. Most people like a balanced look, with 2 10,000K and 2 actinic bulbs. But really it is personal preference. If you like a bluer look use more actinic. If you like more white use more 10,000K. I don't know what that 50/50 bulb would be like. Most 50/50's are half 10,000K and half actinic. The 7100K must be for enhanced growth or something. You might try 2 of the 50/50's and two actinics if you are going for coral growth. That should give you a good balance of PAR and color. Anyway, any combination you choose you can't really go wrong. HTH