For PS2 Emulation, my R9-290 will be limiting my FPS on certain games; while other games run like butter. Slowdowns in emulators are far easier to notice than in regular games.
The CPU part of Core-M will be fine, but some games will definitely obliterate the integrated graphics unless there is a hack-fix in the emulator to help out performance.
My laptop's GT 650m would be crushed by many PS2 games with many, many frame drops while the R9-290 wouldn't in most areas. Then again, some games would feel buttery smooth at 60fps.
Make sure to limit Core-M's turbo-boost if it throttles graphics speed and not to enable too many graphical enhancements in the emulator and it should be O.K.