Afaik, emulation regularly uses 1 single core, that's why single core power is so important and, as extension, why Intel CPUs are so obscenely better than AMD CPUs in that regard.
Anyway, for those up there that said that we shouldn't expect too much from Wii U, i think you're underplaying it too much. Wii was already capable to emulate PSOne to a certain extent with its Broadway @729 Mhz. Wii U has the same Power7 CPU per core @1.24 Ghz. If 200 Mhz made a huge difference with my old Athlon X2, i can only guess how a PSX core will run on Wii U (Well, we already have some examples. Try running Garou MotW on Wii)