Well completly forgot Paste Pump out is a thing, finally repasted my 6950xt AGAIN, and dropped temps to almost 8C between average core temp and hotspot temp.
Figure out what sensors are TMPIN6 and 8 then report back, you have something getting hot. It may be something with the game though. Test with another source engine title.
People don't recommend using a daisy chain cable, but I've personally never seen an issue with it. Depending on what you play look at some reviews and take them with a grain of salt for what your performance will be in games. I run a 6950XT overclocked on daisy chain cables and have no issue even when doing all day gaming sessions at 4k
They are 75% keebs, I personally tend to like 60%. I've built a few myself and the biggest question that comes to mind is. Do you really wanna build or do you wanna do some research on some quality prebuilt options. I've personally tried a few myself and have come across some super budget keebs that really surprise me with the overall feel and build quality but still need a little modding to get the sound I want from when I use it correct.
Something like a 7800 XT? I've personally had alot more luck myself with AMD cards and drivers. The Radeon Software is very nice to use once you get around the semi clunky UI, plus alot of built in things like frame rate limiting and "Radeon Chill" (Locks framerate to drop Power usage) to name a few.
Well since you don't have on board video to see if the GPU went or something with that PCI-E slot is giving an issue or some sort of short. I would recommend finding a cheap used GPU to do some further troubleshooting. There is a chance the Board just failed, but I would recommend testing other components first before doing anything of the sort.