I've made acceptable 8 x 10 prints from colour negatives using both Ilford MG III and IV as well as Agfa MCC. Because of the base fog of the colour negative it is necessary to use a harder grade 3.5 or 4 to build any contrast, in my experience. I also had some rather grainy results which I think were caused by the brand of colour film used, unfourtunately it is so long ago that I can't remember which film I did use.
My experince here seems to be somewhat different.
My photograph, "Untitled", top center of page 2 in the Standard Gallery here, was taken with Agfacolor 400 color negative film, and printed on Ilford MutiGrade IV - Portfolio.
The enlarging exposure was unusually long: On the order of 100 seconds @ f/5.6, when the usual is about 30 seconds. My first test exposures seemed to have *too much* contrast... so the dichroic filtration on my enlarger (Omega D5500) was eventually set to what would be the equivalent of ~ Grade 1.5 or so.
Of course the color-to-black-and-white "coding" is not accurate. I like it the way it is, though - therefore, that is the way it will be.
I never exposed anywhere near that long... maybe that was the problem. Thanks there http://apug.org/forum/html/emoticons/smile.gif