I have a 2600k at 4.5 GHz (probably can go faster, since I haven't put much effort into overclocking). For almost everything I do, it's fine, but some games in Dolphin still push the limits. It's really annoying when something runs perfectly well most of of the time, but has occasional slight speed drops.

25% faster clock-for-clock would probably fix this in most of the games I care about, and that might be enough to get me to upgrade.