I know nothing about the Canon option so I won't speak to it in terms of print quality or routine performance. I have been using an Epson 4900 since the first day they became available in Toronto and I can tell you this: Print quality is really superb and machine construction and performance are extremely robust, however prospective purchasers must bear in mind that Epson designed these printers as production units - intended for quite frequent use. I had frequent protracted absences from my printer over the past eighteen months, and when I return to it, there are clogged nozzles and they need cleaning. My experience has been that one or two cleaning cycles is usually enough to bring it all back to standard status; the cleaning cycles take a couple of minutes or so. It has happened periodically that after the cleaning cycles, one channel may still exhibit some lack of flow. The machine allows channels to be cleaned in pairs. I have done that, and each pair-cleaning takes about a minute or two. I have had only a couple of episodes in the past 18 months where a colour dropped out during a print session, but this happened when the cartridges were very nearly empty. After replacing the cartridges those colours have been well-behaved. Bottom line: excellent printer, but like me you are probably spoiled by your 3800, which could sit around unused for ages without any consequences. A 4900 is a somewhat different animal. If you are usually around the machine and can run a small print or two every several days, you will probably have very little difficulty with clogging. You can read my review of this printer
on this website, followed up by http://www.luminous-landscape.com/reviews/printers/epson_4900_printer_review___addendum_february_2011.shtml
The one thing that needs to be said about Canon's technology in respect of clogging and cleaning is that the design philosophy is different. All of these printers develop clogged nozzles. The difference is in how they are handled. With Epson, the clog announces itself, you clean it and move on. With Canon, they have built spare nozzles into the print-head, so when nozzles clog they get replaced by spare ones. The user does not see this - all under the hood, until the time comes - duration depending on how much you print - that there are no more spare nozzles and you then need to replace the print head. I hear they cost upwards of USD 500 each. So from the point of view of trouble and inconvenience, you get it in batches with this option, rather than in "real-time" with Epson. Maybe you'd never need to change a head till you decide to replace the printer, but maybe you will - can't tell.
As far as using Exhibition Fiber paper in the Canon printer - sure you can; you'll need to get a profile for that printer and paper combination; the best route to go if you don't have your own profiling set-up is to get a custom profile from a reliable provider such as Andrew Rodney (digitaldog) or Scott Martin (On-Sight). You would first buy the printer, generate the target according to their instructions, send it to them, they make the profile and email you the file which you plunk into your profiles folder. It's not a factor that should interfere with a printer purchase decision.