I have had some difficulties keeping croceas (ultra, the colored reg. grade ones did fare better)in the past under 400 watt radiums. If the clam was not up on the rockwork right under the bulb they didn't do so well (slow growth, less color, even some losses). When I would first change out my bulbs there would be explosive growth on all clams but then within 6 months it would severely slow on croceas. Whereas the maximas were always fine on the sandbed- great color, pretty good growth never a loss. This was a 24" tall tank. I honestly think that croceas and maximas retain better coloration/grow better under 10K lighting., this could be just in my experience though and could be related to a number of factors (bulb height, water clarity etc)
I do personally like the look of 14K MH better and they probably would be a better choice than radiums, but I get a bit nervous because of my past experience so I will be mixing 10k and 14k just in case-especially since my new tank will be 30" deep.