Um , which FX- 4xxx do you have ? Bulldozer or Piledriver ?
Multi-Player require much more CPU power
For example . Mario Kart can run full speed on my laptop but MK with 4 players (4 wiimotes) need i5 3570k @ 4.2GHz
Bulldozer suffers from low IPC . Phenom II IPC is better
Piledriver is abit better than Bulldozer
I explained why FX CPU is not suitable for Dolphin here
Overclocking will help you
Multi-Player require much more CPU power
For example . Mario Kart can run full speed on my laptop but MK with 4 players (4 wiimotes) need i5 3570k @ 4.2GHz
Bulldozer suffers from low IPC . Phenom II IPC is better
Piledriver is abit better than Bulldozer
I explained why FX CPU is not suitable for Dolphin here
Overclocking will help you
Laptop: (Show Spoiler)
Mini PC :: (Show Spoiler)