Which CPU should I use?
Dolphin is a dual core application that relies upon IPC (Instructions Per Clock) for performance. Additional cores will not make Dolphin go any faster, though an “extra” core that Dolphin isn’t using may help slightly by keeping background tasks from using the same cores as Dolphin.
Intel: Newer Core i5 and i7 processors such as the i5-4670K and i5-3570K are extremely fast and very affordable considering their relative power. The K series allows for overclocking, which can further improve the performance of those CPUs. Core i7 variants yield almost no benefit in IPC over the i5s they are based on, so save the cash if you’re building a Dolphin machine. For laptops, you can rely on the i7-4700MQ and i7-4930MX for the absolute best performance. Most games will run very well on any of those processors.
AMD: Due to very low IPC, AMD CPUs are poor choices for Dolphin. The FX8000 line of processors is the best they have, and even then most of those processors will be around half the speed of the 4670K’s performance with Dolphin.
Note: For more information regarding CPU performance, please checkout this handy benchmark that contains results from tons of users. Just remember that Dolphin is a console emulator: it does what the games instruct it to do. Every game has its own needs and requirements. Some games run well on most modern processors, while some won’t run full speed at all times on even the most powerful of processors.