What games are you running and what is the spec of your Mac hardware?
For me, in the past, running Dolphin has nearly caused my Mac to catch fire.
I was pulling maybe 15fps on New Super Mario Bros. if memory serves right. (too slow to be playable).
I am primary playing Mario Kart Wii - and we got about 40-50fps for native 1x (SD) and 35-45fps for native 2x (720p). Playing 2 players dropped to about 25-35fps. Most GameCube games play at slightly faster speed.
I am using a lowest end Mac Mini (just bought a few months ago), you can check the spec in Apple Store.