Every emulator will have problems, if you want a correct experience (slowdowns and anything else) you need to play on the actual hardware.

Warrior wouldn't be suggesting RetroArch if it wasn't available for Windows.

He'll also correct me if these links are wrong but, they should be correct:
http://www.libretro.com/
http://buildbot.libretro.com/stable/1.3.6/
http://buildbot.libretro.com/nightly/windows/