How many C'ieth Stone missions should I do in chapter 11 of FF13 before moving on?

I'm slowly chipping away at chapter 11 (very, very slowly) and I'm curious how many of the c'ieth stone missions you recommend doing before progressing the story?

I just finished up mission 5, and I've heard you can stop at 14, 20, or 60(!) depending on the source. I'd like to avoid any major difficulty spikes in the last two chapters, so I'm willing to grind a few of these missions if I have to, but I have no intention of doing any endgame content.