How is the CPU score? Is it performing as it should?
It would be better if you start a new thread in the hardware/modding sub forum with all the info combined. You might get more help this way.
On a second thought - your CPU is 80W, your primary GPU is 100W, this leaves about 120W for the rest of the system - RAM, HDD/SSD, chipset and other stuff including the secondary GPU. So you might be indeed power starved. If I was to undervolt and underclock anything it would be the primary GPU, leave the P5200, after all you want as much performance as possible.
The last couple of pictures are with it soldered. It runs as it ran while testing it, so everything is fine. How it is going to work for you is another story. It seems that I’m the only one to try it on mine and you’ll be the first one to try it on yours, if you decide to do so.
Yes, it has vBIOS chip installed. The wires and the socket were for testing purposes.
I’m not very familiar with dual GPU machines, but I’ve seen someone running the second one as a renderer. Don’t take it for granted though.
It was tested on W10 legacy (non UEFI) and works, so there’s that.