There was an entire thread a while back about overclocking your CPU. NaturalViolence posted a really thorough guide about it too. There are a lot of factors to consider, chief in my eye are temps and overall stability. Overclocking has been common for years, and it's not a dark art anymore as some might have perceived it. In more than a handful of occasions, some computers simply won't reach fullspeed in Dolphin without it, no matter what settings you try.
Also, as Scarface7 said, some older builds "work" better for some people. Some games might play better, but they also might be affected by bugs that have since been fixed in newer versions.
Also, as Scarface7 said, some older builds "work" better for some people. Some games might play better, but they also might be affected by bugs that have since been fixed in newer versions.