AX860 not enough for 3090

[Born_2_Kill_83]

Feel like a need a second pair of eyes on this, I'm also going to post in the PSU section as I'm not sure where the problem lies.

I'm getting power off/restarts in Hunt Showdown, and only Hunt which is the odd thing, I've recently completed 70+ hours in Cyberpunk without a single problem from what I remember. That game has massive media on being buggy so I may of had a shutdown and put it down to the game on that occasion.

My system consists on the below:
3090 (founders) @ 120% power +125 core
8700K @ 5.0g 1.31v (8Pack binned delidded) with Corsair H150i AIO 6 120mm RGB fans
Gigabyte Gaming 7 Z370 + 16GB 3600mhz
3 further 120mm RGB fans for case
Multiple RGB strips and controllers
2X SATA SSD, 1X M.2 SSD, 1X spun drive

I have tried the following:
Checked all cabling to the PSU and MB is seated correctly
Stressed CPU overclock for several hours in Prime95 OCCT, Linpac and AIDA64
Stressed GPU for several hours across multiple benchmarks and games
Re-seated AIO to remove air bubbles
Re-applied thermal paste X 2
Stressed Memory

Max temps on GPU are 72C, CPU highest core in game 78c, VRM 72C.

A online PSU calculator suggests I need a 780W PSU

Now the reason I'm now questioning the PSU while although on paper is should be enough it is over 3.5 years old and has had a hard life. What's more is if I remove my GPU overclock and put it back to 100% power, everything is fine, if I run my CPU at stock speeds all is fine. It feels like I'm hitting a power peak and the system is crapping out. Could I be wrong? why only in one game that's the thing that's getting to me. Warzone fine, Assassins Creed fine.

Thanks for reading my wall of text

 

[mikehhhhhhh]

I think as soon as you start having doubts about a power supply, it's time to change.

The evidence certainly seems to indicate you're hitting power limits that are lower than what the PSU should achieve.

Silly question, but you are using separate cables/rails for each 8pin on the GPU adapter, right?