Use options: -triplebuffer -mt (just for that game)
In newest GroovyMAME sound is emulated at the same speed as video, as it should always have been.
You can't get 100% speed for Donkey Kong running on a standard arcade monitor mounted horizontally as it requires 256 lines (press F11 to check), so the sound gets affected accordingly.
By enabling triplebuffer the game will run at 100%, you will just miss some frames here and there but it won't be so bad for a non-scrolling game like dkong.