That is really odd, as
both of them mostly hammer FPU yet I have never seen Prime95 hotter than IntelBurnTest. Most people use the largest "Blend" setting to more test RAM but the smaller FFT may be more like Linpack.
The only things I can think of is the AVX, which is more efficient but does more work, or the
Skylake bug. Would you be willing to try old version 26.6 from 2011 which doesn't support AVX?
Prime95 is currently running on
1.45 million CPUs, most of them OEM machines with stock heatsinks, and if they were all hotter than IBT I'd think we would've heard something about it by now.