This is a 4 light total set, correct?
I would do 2 03
's and 2 10k's. Should give you a good mix and will make the fish stand out. Going with 4 03
's would be pretty darn purple/blue.
Is 20k's any better for the tank or the same as the 10's the 20k's are $5 cheaper.
Hard to say. The trend seems to be that people are beginning to move to lighting in the higher end of the spectrum and then adding 03
's as well. I am in the process of finishing up my canopy which will include a 250w 20K MH
and 2X55w 03 PC
However there are still a lot of people that use 6500K supplemented with 03
'sa and report great coral growth results.
Bottom line: I think lighting is 75% personal preference. Everyone has a different opinion.