It's 4 color. And everything else is the same as ever other recent Cannon. Dunno what you see in it. Save for the i9100 or save longer for the i9900 and save yourself a few years of replacing printers.
Even my little i450 can do amazing quality on Canon photo paper. You have to see to believe. These top two new ones can do automatic duplexing - you don't have to turn the stack over yourself. You can have two different types of paper loaded and do bin-switching from your documents. If you have the same paper in both bins, it will automatically switch to the other when one runs out. It's hard for me to imagine that anyone less than a graphic arts professional would need more than what these top two models can do.
.bh.
Well I can't seem to figure out if the i450 has photo black. Otherwise if you can't see the reason to go to the other 2 printers I mentioned I can't see there reason to go to the new ones you mentioned.
I mean if as you said you are merely looking to replace an aging printer then sure but why not spend the same amount of money on a 6 or 7 color.
As far as the resolution goes, I haven't seen an "optimized" resolution do any better of a job than the native resolution yet.