Yeah that seems spot-on for gaming thermals with the NH-D15. You can always run a CPU benchmark as a second sanity check to see worst-case thermals, something like Aida64 or ASUS RealBench.
Thanks again for the suggestion, I tested RealBench and got the following:
Image Editing 203113 Time:25.05
Encoding 483949 Time:19.812
OpenCL 106594 KSamples/sec: 2803
Heavy Multitasking 328927 Time:29.733
System Score 259326
Seems fairly close to the benchmarks reported in some sites.