i think that any dual-core cpu is enought to be used on any Android handheld gaming console.
I think with dual-core we have power enought to play anything playable on android.
in fact, today with G18A or S5110 we can play almost all android advanced 3D games, and N64/PSX (not perfect, but playable)
the only thing we need for now, is a NDS or Dreamcast emulators that can use the power of dual-core/quad-core, to justify the need to release an android console with these CPUs, but for now, i think we don?t need more than a dual-core device for these consoles and raise his costs. (for tablets or netbooks may be good quad core)