Help! Okay so what are my options?

[Shonumi]

Just so you know, how high you can raise your Internal Resolution (for HD gameplay) and AA without causing any slowdowns is dependent on your GPU. The rest of your performance is largely on the CPU. So, if your GPU can handle your given IR and AA settings without being the bottleneck for your system, any slowdowns will be CPU-based. An upgrade to the GPU would just give you the ability to make the graphics look better without bogging down your system, but if your system is being bogged down by Dolphin's CPU-bound calculations, a better CPU is the appropriate hardware upgrade.