When you say speed issues, do you mean stuttering? If so, unfortunately that will happen with any computer, even the most powerful one. It is caused by shader compilation. As you progress in the game, stuttering should be reduced.
EDIT: you probably already know this, but Dolphin performance relies more on the CPU than the GPU. Sure, you need a decent GPU to be able to run games with enhancements, but a good CPU is more important.
EDIT: you probably already know this, but Dolphin performance relies more on the CPU than the GPU. Sure, you need a decent GPU to be able to run games with enhancements, but a good CPU is more important.