I have never had the stock cooler fitted but with the Scythe and the Noctua temperatures both at stock and overclocked have been on a par, this also goes for idle/load temperatures. The temperatures withe the Scythe and Noctua are consistent.
Based on that I am guessing:
Not fitted both the Scythe and Noctua heatsinks correctly on several occasions.
The reported temperature is wrong.
The CPU IHS is concave.
Based on that I am guessing:
Not fitted both the Scythe and Noctua heatsinks correctly on several occasions.
The reported temperature is wrong.
The CPU IHS is concave.