I guess you don't follow pre-release Geekbench leaks. Some leaks come from reviewers and are variable, but it's been a pattern for years that there is one early leak that is at the high side of the range, and I suspect they come from Apple itself, to generate press and hype. Geekbench averages for older chips are not very useful as a comparison because they are typically much lower in the curve.
That's besides the point anyway. The main point is that even if you think the single core speed increase is say 9%, 7% of that is attributable to the clock speed difference alone. That leaves all of a 2% difference in IPC. Either that is margin of error from an identical core, or else it's a very similar, tweaked core. Yes, Apple did say there is a potentially a 20% power utilization savings, but we have no idea whatsoever how that's measured and at what spot on the power curve, and it's also on a new process and after a year of improved yields.