As the author of that article, thank you. And, I agree it would be sad if you had to think about exactly how many drives are in a RAID-Z group. The entire point of my blog post is that you do not have to think about it.

"TL;DR: Choose a RAID-Z stripe width based on your IOPS needs and the amount of space you are willing to devote to parity information. Trying to optimize your RAID-Z stripe width based on exact numbers is irrelevant in nearly all cases."