I tested both of these papers today. The Arches Velin Museum Rag is too stiff. It will not fold around the roller in my printer, and jams the device every time.
However, I’ll be using the Rag Photographique in the future. The colors closely resemble those of my proofs, which are run on HP Premium Plus Photo Paper. The primary color difference lies in the the blacks. On the HP paper, the blacks are crisp; deep. On the Rag Photographique, they have the sultry richness found in an etching. It should be noted that, on the latter, the blacks don’t reach their full intensity until the print has thoroughly dried.
Legion was good to its word and sent me replacement Somerset Enhanced Velvet. However, I’m still experiencing a pronounced color shift.