Earlier quoted context omitted.
No, I mean the relative performance and price/performance between z and Power or z and x86 is not public and never will be, so any performance comparisons between mainframes and normal servers have to be treated as rumor or speculation. This is not relevant if you're actually buying a mainframe because IBM will probably let you try before you buy, but it makes armchair architecture (HN's favorite sport) difficult.
In fairness to IBM, that's how enterprise sales usually works. Try finding independent production data on Oracle DB, for example.
Which is a pity, because I look after a bunch of Oracle on zLinux and would like to share...