In 4.0.2, try enabling openCL, as it can sometimes kick the GPU into high performance (although it was removed in a dev build because some people don't see the use of it)
If that doesn't work, the latest current dev build as of this writing is 4.0-539. Try downloading that one.
When you right-click on dolphin.exe, does it give you the option "run with graphics card...." ?
If that doesn't work, the latest current dev build as of this writing is 4.0-539. Try downloading that one.
When you right-click on dolphin.exe, does it give you the option "run with graphics card...." ?