As a counter point to thermal throttling:
Modern motherboard and processors will run as strongly as they can given the workload and cooling capabilities.
If a processor senses a dangerous heat level it will slow down to protect itself. That point for Intel is 100c.
That is a good thing. It keeps you running which is better than a failure.
When the heat issue resolves, full speed can be resumed.
The throttling may be very momentary, perhaps a fraction of a second.
K suffix processors are better binned and will have a slightly higher turbo potential compared to non K processors.
You get what you pay for.
For an ITX build cooling is something to address. Not so much from the small size as for the inability to get lots of fresh air into the system to cool the cpu as well as the gpu and the motherboard.