Doubleposting but I found a better solution for Linux - DRI Prime. Basically the amdgpu driver is loaded for both cards with the significantly less hungry iGPU as primary card. The rx580 in this setup is pretty much off and automatically sent by the driver into D3Hot when not needed where it basically consumes zero power and doesn't produce any heat; I can't really measure any power consumption. (~25W measured at the wall doing desktop stuff, as is normal with my 4650G setup, this includes the monitor, 40-55W it was with the dGPU as primary card, also a lot more heat) When I need the dGPU I just launch the program/game in question with the enviroment variable DRI_PRIME=1 and that's it, the program gets rendered on the dGPU and displayed via iGPU. There is probably some performance overhead and latency added, but I didn't notice it. This feature is mostly intended for hybrid graphics laptops but works just fine on desktops too, there's nothing hardware specific about it. The biggest difficulty was the appalingly poor documentation and tard-wrangling my BIOS to not turn the internal GPU off. Now I have the best of both worlds. Light gaming, browsing etc. on the iGPU, the heavy stuff on the dGPU, and switching is just a variable away.