QTR-Quadtone RIP

With the R1800 3MK set up (3 Eboni and 5 cleaning cartridges) run by a Mac I was having 
trouble with banding in large areas of even midtones. This was prominent all across the print 
in images with a lot of sky, not just the edges, using Premier Art 270 and 325g papers. I 
recalled a post (but can't find it now...) by Paul mentioning he had tried 4MK and gotten 
marginally smoother prints, thought this might help the problem. I added an Eboni cartridge 
to the C position. Having no Idea what I was doing I tried converting Paul's profile for the 
Premier 270 to 4MK: In addition to the obvious edits I cut the LIMIT from 70 to 52.5 for the 4 
inks (sum still = 210 if that is important). I duplicated the CURVE for the GL and used it for 
the C position as well, this was a random choice. I am curious why the original 3 curves differ 
slightly for the MK, PK and GL positions and wonder if a new, different curve is needed for the 
added C position?
Didn't re-linearize.
The results appear very good, the banding is effectively gone, and to my eye the prints look 
otherwise like the 3MK versions. 
Am I missing anything, or is it a safe bet to use this approach in general for getting to 4MK? 
It certainly seems to help my print quality.
Thank you,
Harlan