WereCat

That's either a really bad cooler contact or bad paste application/dry out/pump out

This. VSync is "required" with GSync as in some cases there may still be some minor tearing near the bottom of the screen. If you don't have VRR display then you can use FastSync (NVIDIA) or EnhancedSync (AMD). This eliminates tearing ONLY if your FPS is higher than your monitors refresh rate. It still ads input lag but way less than VSync and the higher the FPS the less input lag you'll get.

what is the power usage during the spike and how many cores are active at the same time?

I don't know but I also don't know what you want. Which codec? How many video streams at what resolution and refresh rate? etc... "max performance" in this can mean anything

IMO the 7800X3D even with just 4060 is a good choice. If he does not need to run high graphical fidelity the extra CPU performance will be nice especially for the sim games. I'd rather look at what else besides CPU you don't really need that much to get a bit more GPU budget.

Which game? Also looks like you did manual CPU OC and therefore reduced max CPU boost clock by around 400MHz.

If it crashes your display driver then all monitors will go black.

Also if you have faulty display cable it's known to caue flicker or outright driver crashing with 5000 series RDNA cards.

Getting 4 sticks of DDR5 working on Ryzen has always been tricky. As I haven't even touched any AM5 parts yet I can only speculate but in my case on AM4 with 4 sticks I have to increase DRAM Current Capability from default 100% to at least 120% otherwise my system will randomly shut down. Maybe you can do it too (but would have to boot with 2 sticks, set it up, turn off PC then insert remaining sticks and try to boot again). You may also need to bump up SOC and VDDP voltages slightly from default. Watch out with the SOC though as you don't want to go 1.3V+ if you're already there!

Can't really compare that as both systems are wildly different. I get what you're saying with the avg FPS being higher on your friends PC but that can be a run to run variance as I mentioned the game performance varies wildly depending at which stage of match youre in, where on map you're located and how many people are nearby. You would have to test the identical scenario every single time to make a more fair comparison as you can have like 50FPS+ run to run variance in PUBG depending on how you test it. His GPU is slower so he will be pushing it harder and thus will have higher GPU usage most of the time than you. His CPU is basically the same as yours. The extra cores you have are not really relevant for PUBG and you will hardly notice a 100MHz difference in boost performance.

PUBG is a CPU and memory heavy game so CPUs like Ryzen 7 5800X3D or 7800X3D will work best due to the large cache pool... almost all battleroyale games behave the same way and performance will always vary wildly depending on which stage of the match you're in and how many players are nearby. There is not much you can do besides overclocking your CPU and memory to get some more performance.

At worst few weeks until the temp starts to creep up due to pumpout after thermal cycling at best 1y-2y before you have to repaste.

It's a bad contact because there is a glue and also because there is a lot of paste spread thick on the die. You want as thin spread as possible otherwise you are just using the paste as insulator instead of thermal conductor. No, knife is not fine... unless you are sure you wont do a single accidental bad move and either scrath the PCB or yourself.

No. TERRIBLE contact, too much space between IHS and CPU. Remove the glue from CPU... Use plastic credit card or somethingike that to remove it.

No, the whole point of deliding is to create as small difference in Z height between CPU die and IHS and thermal paste vuscosity is not good enough and as mentioned, will pump out over time due to thermal cycling. I have experience with LM, graphene pad and PTM 7950. I say go with PTM 7950, almost all the benefits of LM without the hassle and risks. Also read my edit on previous comment.