Can't say that I've heard both, but the biggest advantage of the DP6 over the UP4 is that it is a unipivot with lateral stabilization, pseudo captured. Meaning that it doesn't rock from side to side like all unipivots do.
I do own the DP6 and am very, very happy with it. You can save a bit if you get it in chrome and not gilded gold.
I do own the DP6 and am very, very happy with it. You can save a bit if you get it in chrome and not gilded gold.