Emulator? Its not good idea... You need really powerfull PC for emulator because it's emulating any consol but also Operation system still needs to be powered.
Some emulators take more power to run then others. A GBA or NES or SNES emulator does'nt need much power to run. My phone runs N64 games fine and i dont have a Samsung Galaxy S4 i have a Sony Ericsson Xperia Arc. (sometimes it lags a bit wiht SM64 and SF64)
the PS2 emulator and dolphin are very configurable, if you know what you are doing you can get it to work well. My IPad runs N64 and PS1 easily, and with tweaking my laptop runs PS2 and GC stuff, but I have to set it up differently for each game.
Gaming specific PCs do not emulate well as emulation requires multiple processes.