Based on some recent comments here (from Neile and Josh) I decided to try some Somerset Museum Rag by Legion and ordered a couple of boxes of 8.5x11. Imagine my surprise when I went to the Moab site and discovered they had no Epson 4000 profile for that paper! Anyway I dropped an email to their customer service, had a reply within a few hours offering to do a custom profile. I got the targets and fed x'd them yesterday and got my profile this morning.
Great service, and the paper is lovely.