I'm not a thermal engineer but...
As you can see here:
Delidding the 4790K for a quick look at the TIM - Puget Custom Computers
This rectangle component inside (die - core) that's core exactly.
It's covered by heatsink (TIM) which should conduct all the heat very well to IHS, then IHS should conduct heat to IHS heatsink (this one you put on cpu, or this one put at factory on box cooling), and then this heatsink conducting to radiator.
So Core->Internal Heatsink->IHS->External Heatsink->Radiator
If conduction parameters of Internal Heatsink is good (and Intel claims, they use NGSTIM in 4790k), then heat "loose" between core and IHS should be maybe 10 or 15%.
This might be exactly calculated, if Intel would release:
- Internal heatsink thermal conductivity
- IHS thermal conductivity
- Stock - external heatsink conductivity
Then,
P = power (our TDP is 88W)
d = thickness of internal heatsink layer
S = core surface
delta T = temperature diffrence between core and internal heatsink
For example:
Core "generating" 88W of TDP heat, internal heatsink conducting 84W (4W "stays" at core generating HEAT - our cause of problems) to IHS, IHS conducting 80W (4W "stays" at IHS), then external heatsink, then radiator which doing it's job quite well, beacuse of dimensions and airflow.
It's just approximations of course... but, when everything is working well (heatsinks, ihs) then answer is: diffrence between core and IHS, shouldn't be bigger than material conducting diffrences. Maybe I say 10 or 20%.
If i'm wrong, then let somebody correct me.