Digital BW, The Print

Hi all

Does anyone have any idea how much needs to be printed to purge the K line on a 4800 
(African style).  I have made a simple QTR curve which limits K to 70% (and does not use any 
of the other inks).  I've printed one sheet of pure black A3 (using Faster and 2880dpi).  As I 
am trying to flush Epson MK and replace it with MIS Eboni the difference is not obvious (and I 
want to do some curves/linearization after the flush so would prefer not to be measuring MK 
instead of Eboni).  

Thoughts?  Educated guesses?

Cheers

Steve