I just picked up some Moab Slickrock metallic pearl yesterday. Even after calibrating the paper, it still printed too dark. The reflectiveness of the paper may have fooled the calibration scanner. I'll try downloading their ICC profile to see if that makes a difference. It does give a 3D pop when looking at it from certain angles.
I used their profile but ended up using the slider in Lightroom to make the picture lighter (this was the B&W print I did). When I just printed is as is it too came out too dark.