Nero CD-DVD Speed (not “drive speed”) calculates a quality score from the maximum PIF number only, and doesn’t look at totals or PIE at all.
Is this a reasonable way to score the writing quality?
Well in my opinion it makes little to no sense to calculate a single number representing the quality of a disk - this is effectively an attempt to let the application “think” for you, so you don’t have to look at the different graphs, totals, maximum values and so on and make your own determination.
Personally I would simply ignore the quality score and look at the graphs, but this is more demanding of the user, i.e. of you!