I think it just gets down to personal preference. If I remember correctly, there's definitely certain types of bulbs to use if you're strictly looking for coral growth and not the aesthetics of how it looks. That would really apply more to coral farmers. But for most of us that are just looking for "pretty" corals that grow decent, I believe a mix of actinic (any of the 4xx nm) and white (10k, 14k, etc) will work just fine. I just gets down to how blue you want your stuff to look. More actinics will obviously add more blue. Play with taking individual bulbs out of your fixture to see how the different ratios of white to blue look.
Personally, I've always like the look of 50% actinic lighting and 50% 10k lighting. It gives you that "daylight" look, but has enough actinic to really make those fluorescent greens "pop". But again... it's just a personal preference.
Regarding the 420 vs the 460... the 420 will be a deeper blue than the 460. But I'm not you'd really see the difference.