In my opinion, the PIF's are the most important thing, and are the first thing I look at when I scan a disc. If the PIF's are good then I don't think you need to be particularly concerned about the PIE's - even if they exceed the 280 reference level.
If the PIF's occasionally spike to 16 I don't worry too much about it. If however, there's a cluster of PIF's say 1/4 inch wide or so, and the whole cluster peaks past 10 or 12, then I get a bit concerned. I get a lot more concerned if the cluster peaks to 16 or higher. This situation tends to happen mostly near the end of a burn, particularly when you're burning at high speeds of 12X - 16X.
Assuming importance rated on a scale of 1 - 10, with 1 being trivial and 10 extremely important then I would rate the CD Speed graph with the following weights:
PIE's - 5
Jitter - 5
PIF's - 9
POF's - 10