spmedi,
Im not here to argue how many bulbs, but I do think having two more bulbs will allow you more flexibility down the road. 4 is 'enough', yes, but 6 will allow you to mix and match more blue and actinic bulbs if you prefer more of a 'deep blue sea' look.
For 4 bulbs, I would go GE6500K, blue+, blue+, actinic03
OR, if the 6500K is to 'yellow' for you, use aquablue, aquablue, blue+, actinic. It should look about the same...not as much blue, but then again, not as much yellow/green from the GE bulb either.
For 6 bulbs, I would go aquablue, blue+, actinic, actinic, blue+, aquablue. It will look more blue, but have the same if not slightly more output as the 4 bulb unit. Its the combo I use on my 40B at least.
It also depends on what you want to keep. LPS, SPS, softies, clams, high light, low-medium light?