For the benefit of all those interested in this topic, your post has triggered in my mind an issue you have already explored but needs to be put on the table in a slightly different way.
You start your post by saying "Something that may not be obvious" - well, that is the genesis of problemo numero uno: for something as fundamental as putting paper into a printer, especially in a situation where we are dealing with four feeds, differing sizes, differing thicknesses and differing finishes it can get complicated if it isn't laid out properly; hence especially under these circumstances there should be NOTHING that "may not be obvious". It shouldn't be necessary to have to trick the printer into doing what it should do straightforwardly. If anything about this procedure is not obvious, Canon has a commercial and a moral obligation to all its customers to make it obvious. (Please tell them I said so - that will make them shake in their boots ) For sake of clarity if Canon is reading this material, the OBJECTIVE FUNCTION we are trying to satisfy is that users of this printer should be able to easily understand what papers can fit into what feed option properly and easily with the printer recognizing the choices made and accepting them as such. If Canon can't satisfy this objective function between the firmware, the software and the instruction manual someone there needs to be taken behind the shed for "re-education". (ouch )
Related to the foregoing, "experience accounts" are starting to appear in this thread, which is wonderful. We're getting some valuable real-life feedback which combined with your review provide more information to forthcoming customers - aways a good thing. But some of it causes concern. Wayne Fox mentions earlier in this thread an issue about rendering of detail, which he believes may be affected by excessive saturation resulting from the choice of "Special 4" versus "Special 3". What is this stuff? Apparently it is related to how the ink reacts with the paper choice. It seems we are dealing here with something that is conceptually different from what one finds in the Epson driver, and therefore another element of the adjustment set to be on top of - but again, that is facilitated with clear, detailed instructions from the manufacturer about what these special setttings do to the ink and the paper.
And perhaps more fundamentally underlying both of the above factors, in this day and age with virtually every customer wanting to use a whole variety of papers (one of the main reasons to buy this machine - no ink switching), Canon again - if they had solid commercial horse-sense - they would realise this and design the paper settings to be "brand-agnostic" and user-friendly for selecting the media type of our choosing. This way we would be quite at ease buying the Canon printer, buying their inks, and print happily onward on the media of our choice without mental gymnastics. Where the rubber hits the road on this issue is the point at which the need to fool around blind-folded with paper options and inking levels can impair the outcome of an otherwise properly colour-managed workflow.
Canon's commercial success with this printer and its successors could well be affected by how quickly and effectively it responds to these issues, assuming they are real issues.