if you love tangs like, i do... get the the sohol or pbt. they look so nice swimming, especially when you have the right lighting. it brings out the color of your fish. overcrowding is really not a problem, imo... with the amount of fish i have in my tank. you would think i'm having problem keeping water perameters in range. the tank is about a year old and i've never had any problem with with water perameters. I did have an outbreak of ich for awhile, but added a uv sterilizer, do regular water changes and within 3 weeks, ich was completely gone. I am planning to set up a 300g within a year or so. most of these guys are going to there.
you should be more concern with the yellow or purple not get along with the new addition. how big are your tangs? maybe go with a bigger tang.