Frame Rate Drop -- New Dolphin Ver.

[smoovieb]

So I upgraded my Dolphin from 3.5 to 4.0-648 to be able to use netplay for Super Smash Bros. Melee, but found that my framerate dropped from a stable 60FPS to an average of about 30FPS on the new version, rendering the game unplayable. I've fiddled with all the video settings I possibly could, there doesn't seem to be a fix that I can figure out on my own. Is there anything I can do, perhaps downgrade to another version?