If you are looking for a computer with a tiny footprint, make sure you read this review of the ECS LIVA Z before you head out shopping. Trust us, you'll be glad you did.
Finishing up, the LIVA Z powered by the Pentium N4200 SoC is your best bet for performance. While not cheap, it does have 4 Cores and the HD 505 with 18 Units. It also holds some architecture features found in the Kaby Lake CPU series, making it newer and more powerful than the Celerons running Skylakes HD 500 series. I have an i3 laptop nearly four years old now using the HD Graphics 4000 with 16 Units and it can play 4k video just fine. Therefore, I have no doubt that this Pentium variant will also.