I too would say temperature difference up to 20c is fairly common on these CPUs. I don't have any numbers to give while at work, but:
I have the 7740X, 7900X and 7980XE. All are delidded using Conductonaut. The 7740X and 7980XE have custom copper IHS on them. 7900X doesn't have any glue left on the PCB and the others still have it.
On the 7740X, all cores under Prime95 are within 5 degrees of each other. On the 7900X, one core is always significantly hotter. On the 7980XE, a bunch of cores are significantly hotter. Also on the 7900X and the 7980XE I would say 1.2V is getting to the limit voltage-wise where you want to be if you want to run Realbench or old Prime95 on custom water. On the 7980XE, 1.15-1.18 V is closer to truth. If you want to OC further, I would suggest setting a bunch of cores to higher clocks and when all cores are loaded leave them to like 4.0 - 4.2 GHz.
I think the 7900X is the worst of the bunch with the highest core count but the smallest die size to dissipate all the heat. I would definitely recommend using this chip with the der8auer direct die kit, it would result in the lowest temps for me so far of any methods. It is true some of these chips can't do even 4.5 GHz, my first 7900X was really bad and it needed around 1.24 V for 4.5 GHz on custom water, resulting in very high temps, and this new 7900X could do Prime 4.5 GHz at only 1.16V so there is a big variance. Also, new chip can run Cinebench at 5050 MHz on cold water...
🙂So much money spent and so much trouble for Intel not wanting to solder the Skylake-X chips. I always feel sad when firing up my HTPC with the 6950X...it runs so cool even on old 240mm AIO.
Main: i9-10980XE - Rampage VI Extreme Encore - 64 GB G.Skill Trident Z Royal 3600 CL16 - Strix RTX 3090 - Phanteks Enthoo Primo - Corsair AX1500i - Samsung 960 PRO 1 TB + Intel 600P 1TB - Water cooling
HTPC: i7-6950X - X99-M WS - 32 GB G.Skill RipjawsV DDR4-2400 - GTX1050TI - Bitfenix Pandora - Corsair AX860 - Intel 750 400 GB + Samsung 1 TB 850 EVO
All around: i9-7980XE - Rampage VI Extreme - 64 GB G.Skill 4000 CL18-19-19-39 - Strix RTX3090 - Phanteks P500A - Samsung 960 EVO 512 GB - Water cooling