I did some lightfastness testing of my own a few years ago. On the expensive offset print issues I had paid for, I got 47 years before fading became visible. I got up to 500 years on some pigment transfer prints made by Bill Nordstrom when he was just starting off here in Sacramento. His website is: <http://www.laserlightprintmaker.com/ gicleeprints.php>, and he is a real old timer who knows what he's talking about. At that point the summer sun was going and I didn't think another year of testing was worth climbing up on the roof for, and lost interest in making them fade. But the prints were very expensive and at prices I could get, not really viable for me. I sold two of them for $700 apiece and probably broke even.
Since then I've trusted Wilhelm Research, which gives the Ultrachrome inks and the papers I've been using 100 years or more, and have figured that was good enough for practicality because the images would last longer than either I or the buyers.