Ink stability 4000/600 and 800 series

[mcbroomf]

I have an Epson 4000 that I need to reprofile due to a slight increase in Cyan over the last few weeks.  I use HM Photo Rag 308 exclusively and the current profile (Cathys) was made about a year ago.  I have a few questions about how often you need to reprofile your printer(s);

1) If you have an Epson 4000/7600 or 9600 how often do you need to reprofile?

2) Same question for those who have Epson *800 series wide formats.

3) Same question for owners of the Canon i5000

Thanks,

Mike