So, following my request for input on possible #x86 based #SBC solutions, the following were mentioned to me (thanks to all who responded):

Atom Pi
Bifferboard
LattePanda V1
Zima Board
Odroid H3+

and the Rock Pi X I mentioned myself.

Unfortunately, with the exception of the Odroid H3+, none of them seem to be easily available here in europe (germany) at the moment. And the Odroid H3+ is quite impressive but at ~250€ rather expensive.

See, what I want to do is replace the Pi3 B+ I'm currently using in this #C64 case along with the #RetroPie distribution. I built this around 2013, starting with a Pi 1 Model B and used it for #retrogaming. But now I also use #Kodi with it and I'd really like the hardware to have just a little more punch.

Maybe I should try and get some #microITX #Celeron or #Atom mainboard and try that instead. If it fits. But that would require a barrel connector on the mainboard. Not every miniITX has one, right?