Dolphin runs best on a quad core cpu with a high single thread performance. Your cpu has a low single thread performance(like all amd cpus) and 8 cores. Half of your cpu is not used in Dolphin, which explains the difference between pc games and dolphin.
Update to the latest Dolphin version like Link_to_the_past told you, that runs much faster than 4.0.2.
Since you have a nvida gpu, try opengl, that should be faster than d3d for you.
And if nothing else helps, create a hotkey for switching between efb to texture and efb to ram. And then switch to efb to texture after you started the game. This should run faster, but it will break pictures taken with the pictobox, so make sure to switch back when taking pictures.
Update to the latest Dolphin version like Link_to_the_past told you, that runs much faster than 4.0.2.
Since you have a nvida gpu, try opengl, that should be faster than d3d for you.
And if nothing else helps, create a hotkey for switching between efb to texture and efb to ram. And then switch to efb to texture after you started the game. This should run faster, but it will break pictures taken with the pictobox, so make sure to switch back when taking pictures.