I'd not noticed that, however I didn't really compare the output of my iPF8300 to the 6450 I was testing until after making profiles, and even then it was only a fairly high level check. I don't have the old profiling targets from when I set up the 8300 and running the 8300 comes out of my own pocket ;-)
There is a difference in the B&W print mode, which suggests there would be in the colour. A few direct comparison prints with the 8300 didn't show enough though for me to want to test further.
I always assume that if I go from one series of printer to the next, there will be some difference - hopefully positive.
I do have to admit though that you'll never get many detailed numerical comparisons and analysis in my reviews, my patience usually runs out long before that sort of stuff ;-) I did measure quite a lot of prints in the B&W print mode though.