The 9500s are limited to 23 inches long in a custom size. However, that's a mere 4 inches longer than 19 inches, and most people do not want to cut their own custom sheets from rolls. The printer manufacturers really prefer that people use standard sizes.
BTW, I t/t the Pixma Pro support guys a few days ago... the 9500 MK II differs in the head and firmware, to increase print speed. it also has the (Vista-only) room light control where by you specify what light your print will be displayed in and the printer biases the print for that. Since room lighting changes (as opposed to gallery lighting which is more consistent) i think that's a gimmick.
At least Canon listened to folks squawking about the glacially slow print speed of the 9500 "Mark I". The head and firmware are not, according to Canon, backwards compatable. Same inkset, same 35 mm art paper border. I'm not planning to "upgrade" and since I will never touch Vista, that room-light feature ain't gonna sway me.