melee running at half speed

[Helios]

Is vsync turned on in Graphics?

Turn it off.

Then go into the NVIDIA control panel -> Manage 3D settings -> create a profile for Dolphin.exe -> in that profile set preferred power management or whatever to "prefer maximum performance" and v-sync to off.

Also, if the profile gives you an option to chose which GPU to run dolphin.exe on, pick the nvidia one.