I think it is always useful to have hard data rather than someone's subjective impression. I love the look of platinum/palladium, and there are certain subjects for which it is the perfect medium. The same is true for Azo.
In regard to the D-max of platinum, there was a recent post on the Bostick & Sullivan forum regarding Mars All-Purpose Translucent Vellum paper. It is said to have excellent wet strength and to give significantly better blacks than other papers. There was speculation that the deep blacks are due to its translucent nature, which allows light to penetrate into the depths of the paper.