I think when I was running 5GHz on Z97 OCF a few weeks back I managed to get 5003 (bios setting) to stay at that freq or lower in OS (highest it went was 5003.36 I think). Turning off force OC and speedstep, but leaving on turbo boost or something. I didn't check how it fluctuated under load though.
I would recheck now, but my OCF is half dead as the back PS2 and USB ports don't work.