No overclocking is NOT over rated. If its a gaming PC you'll get real world noticeable performance improvements with a faster cpu. My fps goes up by around 20-35% in some games.
I don't see how this is possible. Looking at benchmarks it's clear that fps in games is almost entirely dependent on the GPU. The CPU just doesn't make enough difference that an overclock could give that kind of jump (unless you're playing on 800x600 res for some reason perhaps).