Thank you all, and thank you Rand for the kind offer. My local dealer has a 9500 in his offices, so I will be able to run my own tests at some point, but it is helpful to hear your thoughts. I am asking more from curiosity than any expectations the the results will be noticeably worse.
Regarding very thin papers for bookmaking, I have made artist books using Awagami papers on the P9000 and did an exhibition of my work on 170x220cm scroll paper at 45gsm (using two rolls and combinging them banner style). The handling of very light and very thick papers is a big concern for me as well, and the more automatic and closed gap loading are less features than worries for me. I would rather have a more open and transparent manual loading system, rather than one that is more automated, as these printers tend to do whatever they feel like at all times anyway...if it works, it is great, but when it does not, it leaves you with very little you can do about it.
So suffice to say I will be testing the Awagami papers and Hahnemühle papers to see how they are handled. I have used Epson papers perhaps five or ten times in the last twelve years of doing this professionally. If the P9500 cannot handle fine art media, then it is worthless to me and my clients. My hopes are pretty high that it will handle them just fine, however.