[Troy F]

do we go with bad colour, but good growth
No, you go with what is pleasing to you. For what it's worth; the Iwasaki bulbs look just fine with a little actinic supplementation.

or do we go with nice colour and ok growth
Again you go with what best suits your intentions. If you can afford to replace bulbs more frequently and don't care how fast your corals grow; buy a higher kelvin bulb.

if we want to provide what is best for the corals shoulden't we all be using 5500K bulbs?
Nope, we'd all be using the Iwasaki bulbs or not keeping them at all ;) .