The FA Pearl contains OBA's while the PR Pearl does not so unprinted areas are not as white.
If you buy these papers by the roll, the cotton rag based papers (PR Pearl) seem to relax or flatten a bit easier than do the alpha cellulose (FA Pearl) papers.
One of the biggest differences, as I see it between the Han PR Satin and the PR Pearl relates to the use of black inks: MK for the PR Satin and PK for the PR Pearl. If you have much detail in the dark areas of your image it will be lost with the MK Black which blocks up very quickly in the dark areas. In the unprinted areas, the PR Pearl has a smoother appearance while the PR Satin is more matte-like.
The PR papers have a more delicate surface than the FA papers, and it is my impression that the PR Satin is more delicate than PR Pearl, so the printed surface needs to be protected.