The definition of "Max T-Junction" from Intel is as follows...
 
"Tjunction max is the maximum thermal junction temperature that a processor will allow prior to using internal thermal control mechanisms to reduce power and limit temperature. Activation of the processor's thermal control system may cause performance loss as the processor typically reduces frequency and power to prevent overheating. The goal for a system builder or a do-it-yourself (DIY) end user is to design a platform configuration that keeps the processor under the Tjunction max threshold during heavy workloads to maximize performance of the system. 
The benefit to a user is that many third-party utilities can monitor the digital thermal sensor (DTS) on the processor die to see how close the system is approaching the Tjunction max temperature without any destructive testing. We recommend that end users look up information on the product specification page (ark.intel.com) to aid them in system assembly. Original design manufacturers should consult the nondisclosure agreement (NDA) documentation available to them for full details."
 
Yes, T-Junction is the max temp of the CPU before thermal throttling will start to take place. When overclocking there is a lot more to the process than just setting a high frequency and high voltage so that its "stable" performance bench marking most be done to see if there is any actual performance gain. I can only assume that the CPU in the examples you mentioned above were throttling and down clocking to a lower frequency without the end user knowing. 
 
The "CPU Die" temp provided by EVGA is not the same temp reading as the CPU Core Temp. You want to use the CPU Core Temp... X299 in general does not play nice at temps above 80C. As the temp of the CPU increases more voltage is needed to keep it stable and as the voltage increases the temp rises creating a cascade...  
 
Also make sure that TJMax is set correctly in the BIOS on the X299 Dark, typically it does not set this correctly and needs to be manually set by the user. If this value is not set correctly the temp readings from applications such as HWInfo64 will NOT be correct. 
 

glocked89
Hey thanks for the reply!
 
Yes 86c seems to be the maximum core temp, but at Tjunction for the the series such as the 9900k, the CPU will definitely throttle. This doesn't seem to be the case with x299 7, 9, and 10th series. The reviews are well documented and the 10980xe seems to hit core temps well past 86c and not throttling at all. This is what led me to believe that T junction provided by intel was different from core temp. T junction by intel is: "Junction Temperature is the maximum temperature allowed at the processor die." and yet the CORE temps are allowed well past 86c with no throttling.

Core Temp as far as I know represents the "processor die" temperature and is the same value that the processor uses to throttle the system. Do you have links to these reviews/videos showing core temps this high? Would like to take a look to make sure that we are all talking about the same value. 

https://elmorlabs.com/index.php/2019-11-26/intel-core-i9-10980xe-5-ghz-on-18-cores/
https://www.youtube.com/watch?v=H0vLYcPa3uk
 
Here are a couple. Gamersnexus' is quite long but he states that he increased the tjmax to 105 or something to allow for those clocks.
 
Yes my x299 dark was actually at 103 and I manually changed it to 86c.
 
Also, because intel has the 10980xe only at 86c Tjunction, have I possibly made some irreparable damage to my cpu going to 103 on some cores?

jasoncodispoti
The definition of "Max T-Junction" from Intel is as follows...
 
"Tjunction max is the maximum thermal junction temperature that a processor will allow prior to using internal thermal control mechanisms to reduce power and limit temperature. Activation of the processor's thermal control system may cause performance loss as the processor typically reduces frequency and power to prevent overheating. The goal for a system builder or a do-it-yourself (DIY) end user is to design a platform configuration that keeps the processor under the Tjunction max threshold during heavy workloads to maximize performance of the system. 
The benefit to a user is that many third-party utilities can monitor the digital thermal sensor (DTS) on the processor die to see how close the system is approaching the Tjunction max temperature without any destructive testing. We recommend that end users look up information on the  (ark.intel.com) to aid them in system assembly. Original design manufacturers should consult the nondisclosure agreement (NDA) documentation available to them for full details."
 
Yes, T-Junction is the max temp of the CPU before thermal throttling will start to take place. When overclocking there is a lot more to the process than just setting a high frequency and high voltage so that its "stable" performance bench marking most be done to see if there is any actual performance gain. I can only assume that the CPU in the examples you mentioned above were throttling and down clocking to a lower frequency without the end user knowing. 
 
The "CPU Die" temp provided by EVGA is not the same temp reading as the CPU Core Temp. You want to use the CPU Core Temp... X299 in general does not play nice at temps above 80C. As the temp of the CPU increases more voltage is needed to keep it stable and as the voltage increases the temp rises creating a cascade...  
 
Also make sure that TJMax is set correctly in the BIOS on the X299 Dark, typically it does not set this correctly and needs to be manually set by the user. If this value is not set correctly the temp readings from applications such as HWInfo64 will NOT be correct. 
 

Somewhat related question on this topic. I just bought an X299 Dark to pair with a 7900X and SLI 1080 tis I found on sale. When stability testing I keep getting reboots without any kind of error, which I thought was the GPUs (definitely not the PSU as I went overkill with the Corsair AX1600i). I had TJMAX in the BIOS set to auto. I'm wondering if the motherboard was automatically rebooting the machine w/o warning because it thought the CPU was hitting TJMax due the bug using "auto." I just set the TJMax to 95 and am retesting. Thoughts on this from your experience?

Why is auto setting for Tjmax set to 105 also in my EVGAX299 MICRO2 ? I've once reached this with CB20 Multi test and it started throttling but did not shut down. Now Im just discovering this as topic. Reading x299 OC guide it should be set to 95 for Skylake-X, but I've read that monitoring software may show wrong temperatures when changing it. Intel spec declares only 85 for my Skylake-X 9960x. Is there any truth out there? :) My CPU is doing well, but it would be insane business that default settings can arise any danger to CPU. Latest BIOS update even lets to set this to 110 but I have no idea why hardcore overclockers need that as they have real nice cooling available and high OC needs normal temperatures to my logic.

Alright, thanks for your answers! Many of the new experiences I read about Cascade Lake-X (and X299 in general) are telling they still hold TJMax pretty high, tons of info to read:
 
https://www.overclock.net/forum/5-intel-cpus/1632870-skylake-x-kaby-lake-x-combined-discussion.html
https://www.overclock.net/forum/5-intel-cpus/1737048-intel-core-i9-10980xe-5-ghz-18-cores.html
 
Last topic shows clearly that 105 TJmax automatically is very common and people not realizing at first that it's not meant for long-term use if we really conclude that. Same time, its not been issue anyway - no real complaints. I now myself realize also that AUTO voltage for my CPU is under load 1.3 or even 1.32 volts for some cores that is also a bit high and 1.2-1.25 may be enough with much more lower temperatures as I read from experiences in web. In my case - max non-oc (If I trust EVGA bios auto-detect) multiplier 45 for 2 cores (Turbo Boost 3.0) and 44 for others, and it works. If I look specs for my 9960x there is actually no info at all what is the all-core max speed Turbo Boost 2.0 from Intel! Take a look at LGA2066 wiki - https://en.wikipedia.org/wiki/LGA_2066 
I don't wanna go really offtopic, I try to read and learn more and Im thinking about writing little guide in some time.

Actually, diggin more in the web -  there is BD PROCHOT that takes responsibility to switch off CPU in case of emergency situation with high temperature. Going beyond TJmax is just speeds up degradation of CPU, with HCC LGA2066 CPU-s have this lower than 4-8 core CPU-s.

Some Intel overclocking engineers did an AMA on reddit and I was actually able to get my original question answered by someone who actually worked on the Cascade Lake X extreme edition processors.
 
"The 10980xe is a very similar processor compared to the 9980xe and the 7980xe but only has a tjunction of 86c.
Why is the tjmax so much lower for Cascade Lake X?


level 2 
whitesic

This isn't a concern for Overclocking. We allow TJMax Override up to 110C for Cascade Lake X, which should be an option in your BIOS, and our customers can configure the defaults based on their design goals. At the same time, I would stress that 110C is not a temperature I would want to run at on my personal machine. :)"

I have set now my Tjunction in bios to 95 degrees because I use long all-core workloads like video rendering with Premiere that can take up to 15 minutes for 30 minutes of 1080p60 video with 16-core 9960x. It will stay nice in 95 degree limit and dynamically lowers clocks a bit to stay at that temperature range.