Alright guys, this might be the biggest noob update ever, and I am pretty ashamed to post this but - I think we solved the problem.
After taking the board out to check for trace rot (thanks ShinGoutetsu) I noticed this chilling near some mosfets in the back near the AV out / back fan https://imgur.com/q6WJnlL
This 'bullet' some might recognize is from one of those cheap solder suckers you get on Amazon. They work okay, every now and then you gotta declog the plastic tip of built up solder, and this is the form it takes... yeah...
Needless to say I've been plugged back in and booted for close to 30mins or so, with no signs of artifacting... back fan seems to be emitting warmish air, so once I 'finally' get this thing truly softmodded I will see the temp readings (how accurate are those btw?)
Thanks again guys, and maybe this will help someone down the road, or at least have ppl be more cautious on their workbench.
Cheers