I want to stay 25c below TJmax.
Hearing something doesn't make it true... and even if it is that doesn't make it safe. I guess I have to ask do you think Intel would spec a Tcase of 67.4c and than supply a cooler that will run the stock CPU at 90c +?? Even with 67.4c + 10c that's only 77.4c, not 90c +. If someone is getting 90c + on a stock cooler with a stock CPU my guess is their case is getting very hot.
Tcase is the temp at a point in cooler just above the surface in middle of CPU. You would have a hard time building a cooler setup to monitor it.
Tcore is at the CPU chip cores.. estimated to be about 10c hotter than Tcase.
TJmax is temperature the CPU throttles is speed or shuts down so it does not get any hotter and burn up. Like a car shutting down when it runs out of oil or coolant... and engine often is still damaged.
Here are some links you read up and learn from