Yes, I really wanted to mount the radiator on the front but unfortunatelly there wasn't enough space, so I have to deal with the GPU heat affecting it. Running aida64 without the GPU stress test gives me a better temperature. However, I don't see that as being the reason for the difference between the average and peak, as the CPU itself is affect indirectly, because what is being heated by the GPU is actually the radiator and therefore the liquid. Once those temperatures have stabilized, those spikes should be the CPUs own "fault".
Temperature spikes have been increased since Intel stopped soldering the IHS to the CPU. The temperature spikes are due to how fast the CPU's run and the rapid changing in the CPU voltage and utilisation and where that utilisation is occurring. Some parts of the CPU produce more heat than others.