The impossible to solve overheating problem

Everything I read here and taking into account all the symptoms would make me VERY suspicious of the water pump.
I have even seen some that the impeller came loose from the shaft.
If this is the case then coolant isn't circulating, and would cause an overheat under any circumstances, and with any radiator or any of the best parts out there.

Note that a gasket leak or a crack somewhere would cause coolant to be pushed out from building pressure just before it overheated.
If it doesn't puke coolant it probably not a compression leak.
(A radiator pressure tester will confirm this one way or the other, without needing to send a coolant sample away)