Well I got the RX 580, I knew going in that it's not exactly the most efficient GPU there is but the data really isn't great. Measured at the wall about 20-25W higher power consumption doing normal desktop things vs. the 4650G Pro iGPU. Fan spins up and turns off at random times which is really annoying but I guess just how the GPUs' BIOS temperature curves are set. Playing back a video the power consumption shoots up to about 75W, which is vs. ~29W with the iGPU, also video playback without annoying fan noises isn't possible. What irks me most is that normal desktop operation is so inefficient. I tried tweaking the power states a bit but it doesn't really make a whole lot of difference. I admit that the case isn't ideal for this graphics card and a bigger, better ventilated case could probably pull off zero fan operation in desktop mode. (I tried forcing the GPU fans off but that just makes the card overheat very slowly) The power consumption still would be much worse. I got really used to my entirely silent iGPU system that sat in a nice corner, temperature-wise and even in the games it ran well merely sipped energy. (playing e.g. Stellaris was a 35W deal, also completely quiet) This just feels very inefficient and crude in comparison. The games I wanted to play it runs very well but everything else is just more noise and heat and costs with no real upside. Also looking around for similar experiences this high power consumption with the card doing nothing really might actually be a linux problem, seems like the kernel people care even less about superfluous power consumption and heat than AMD does. I could live with the added power consumption, but random fan noises doing normal desktop stuff and light gaming/emulation after the paradise that was the iGPU? No deal.
One way to deal with this could be to just pcistub the card in linux and just activate it with a VM or similar passhrough for the specific use cases I have and for everything else, use the iGPU. That just feels like a lot of added complexity though. My guess is I'm going to sell it and just wait until iGPUs get where I need them. I feel that won't take long to begin with.