Well I would recommend a Celeron/Pentium or Athlon. Well worth the premium, because Atoms are really slow and Semprons/Celeron (single core ed.) consume about as much power as the dual-core variant.
I would probably buy an AMD motherboard without EFI, as most Intel motherboards have EFI. Perhaps check if there is an option to not enable it. My motherboard will cause a kernel panic with EFI enabled, but I can use BIOS emulator legacy boot.