I would not trust this paper by Bob Fernner. He is clearly out of date in this paper. All you have to do is read what he said about MH in it.
Rather than this I would direct you to the many papers by Dr. Sanjay Joshi that can be found in the link below. Sanjay is an avid reefer and an Doctor of Engineering and a professor at Penn State. He extensively tested and wrote about MH lighting. Any serious aquarist who use or contemplate using MH light should spend sometime and read these articles.
Essentially according to these test, MH output decrease with time at all wavelenght. None of the wavelenght increase in intensity. Higher frequency wavelenght tend to decrease a little faster. At worst bulb, the intensity of light decrease by about 30% at two years. Anyway, I encourage the OP and anybody who follow this thread to read these series of articles, original publish by Aquarium Frontier and Advance Aquarist.
The major limitation of these studies is that he use different bulbs of the same brand at various age, not the same bulb at various age. Apparently there is significant variation from bulb to bulb of the same brand. Reading these articles help me a lot in determine which bulb to use and how often to change them. Read them and draw your own conclusion. Happy reading.

Here is the link:
http://www.personal.psu.edu/sbj4/aquarium/articles/