I used to be a fan of Hahnemuhle Photo rag until I noticed variations in colour between different roll sizes and different batches of paper. I have found there is even a very distinct difference in colour results after printing between the Hahnemuhle Photo Rag rolls and the Hahnemuhle Photo Rag Duo sheets, and have consequently had profiles made for the Duo sheets - even though to the best of my knowledge it is supposed to be the same coating as "Photo Rag" . Perhaps different mills and 'factories' are producing slightly different coatings even with the same 'recipe'.
I have custom profiles made by Les Walking and it was infuriating changing rolls and finding that the prints had variations in tonality or colour.... just marginally... but quite distinct and totally unacceptable when producing the work I make.
I then out of desperation tried Canson Rag Photographic and found it to be an absolutely beautiful paper - although a tad too smooth for my own preference, since I quite liked the tooth of the Hahnemuhle Photo Rag. Choosing the compromise between having a texture which wasn't totally what I wanted , and having slight differences in colour between rolls was a no brainer for me...and I went the consistancy route.
I haven't tried the Arches Vellum Museum Rag, but am using the Canson BFK Rives for some artist books, and this paper has a lovely feel when held and quite a beautiful texture which I like. I am experimenting with using this paper instead of Canso Rag Photographique for my next body of work, looking at the landscape and geology - where the texture of the paper I think may contribute to the overall 'feel' of the image and what I want to create.
I would suggest though whenever choosing a paper, I firslty hold it in my hand to determine its' physical characteristics. I then would look at the technical data and specs to see the DMax etc.... then I would get a profile made. I wouldn't wste any ink printing images before then because unless you work out how to get the best out of the paper by using a custom profile, you really can't determine the potential of the paper. Once the profile is made, I would test a couple of images using a couple of different papers and get someeone else to put them up on the wall so initally I don't know which is which.... sort of like a blind trial with my eyes open... (LOL - bad pun I know)... Then over a couple of days work out which image has the best 'presence'.... and that would be the paper i would go with for that particular style of image or body of work.