There are several potential problems with high OBA papers:
They will eventually burn out, and when that takes place they will often be darker than unwhitened paper. Also the colors were applied using a profile created when the paper was white, so there relationship between the paper white and the image also changes.
To prevent OBA burn out, you could mount under UV protective material (UV glass or spray coating). Unfortunately, optical brightening agents require UV light to fluoresce. That is how they work: they take in light in the UV part of the spectrum and reemit it at the blue end of the visible spectrum. UV protective materials don’t stop 100% of UV, so still get some of the brightness.
Some high OBA papers degrade very quickly, and other don’t. It seems to depend a lot on where the OBAs are: in the paper base or in the top coatings. Epson Exhibition Fibre, for example, has very poor paper fading characteristics. The Epson ‘Pressed’ paper do not seem to suffer so much in this regard.
As for paper choices, I believe they do samples. If you haven’t used the papers yourself, you really need to see samples. Or you could get a Moab and Epson sample packs and print smaller ones of the image in question.
They do seem rather highly priced, unless their shipping is very low. And you should be able to find printer that does a baryta or two. Unless you live in a town of less than 50k, you should be able to find a local printer to work with you.
[I have also PM’d you.]
Brian A