I've been using my new iP4600 with factory profile (BTW, no useful documentation of profiles and naming conventions are utterly useless). The results with my best guess at correct profile were surprisingly accurate for color, which really encouraged me. I'm printing on Canon glossy photo paper.
The one problem I'm noticing is that, while shadows don't look as black as with the Epson R1800 on Epson glossy paper, I'm simultaneously losing shadow detail because shadows are more blocked up with the iP4600. So, paradoxically, I have less shadow detail but areas of solid, dark shadows don't look as dark. If I compare the same print side by side, Epson vs. Canon, the Epson print has much more "snap" without losing any highlight detail, and it has noticeably better shadow detail.
I've turned off all color management in the printer driver, I've let the printer driver control color, I've used every combination of settings, and nothing seems to make any real difference.
I'm waiting for a custom profile from Cathy's Profiles, which really made a difference with the Epson, and perhaps that will help here, but I wouldn't expect a custom profile to affect shadow detail, only color accuracy.
I'm stumped. Thoughts?