I had little luck finding information specific to the iPF5000 in the forums so I took time to do a little testing and although the observations are subjective I am pleased with the results. All tests were done with the following constant. 17"x22" Ilford smooth gloss, 16 bit 600ppi, 8.5x11" file.
1) Printed with the Canon windows print driver, Qimage and the Canon 16 bit plug in (16 bit, high accuracy, 16pass 2400dpi); the 16 bit plugin was superior.
2) Used canon profiles and custom profiles (Cathy's Profiles); The custom profiles were superior.
3) sent the 16 bit plugin a 300 ppi 17"x22" file, a 600ppi 8.5"x11" file (let the plugin size to fit) and sent the plugin a 600ppi 17"x22" file upsized twice in CS2 using bicubic smoother; the latter was superior.
4) Used both perseptual and relative colorimetric rendering; relative colorimetric was superior.
In summary use the plugin, a custom profile, upsize the file in photoshop to 600ppi resolution, actual print size and use relative colorimetric, The difference between the drivers, rendering intent and profiles was more than subtle, the difference in upsizing method was slight but noticable. My conclusion is sending the printer 12 bits of data makes a difference. I hope this saves others some paper time and ink.