I've had a FX-8320 for some time, did a bit of OCing @ 4.00GHz but have now returned it to default settings. When overclocking it to 4.00GHz, in Windows 8 x64 it'd always show as 4.01GHz while running at 3.98GHz, and now I'm running it at 3.5GHz (Windows reports 3.51GHz) and it runs at 3.48GHz.
This is really irritating behavior and I don't know why it does this. A few OS installs before, it would exhibit this behavior occasionally after settings changes, but I don't remember after what.
I have turbo, AMD Cool'n Quiet, C1E, C6, and HPC disabled.
There's also a setting called "Enhance Power Down" but it's undocumented and I can't find it online.
Thats just how it is. Clockrate just isn't accurate to the same exact decimal. I have a 3.0GHz Pentium 4 - its really at like, 2.992GHz. It's not a big deal, its normal, don't let it get to you. You aren't losing any framerates or performance!