CPU-Z is not very accurate at reporting the multiplier, especially at idle.
i7 Turbo can accurately report the multiplier for each thread in real time using the method that Intel recommends in their November 2008 Turbo White Paper.
Here's the latest RealTemp beta download which includes the i7 Turbo program.
http://www.fileden.com/files/2008/3/3/1794507/RealTempBeta.zip
If you are using Vista or Windows 7, remember to go into the Control Panel -> Power Options and set your Minimum processor state appropriately since this also controls the multiplier you'll end up with at idle.
When all of your power features are not in agreement, you can end up at idle with a multiplier that cycles up and down continuously on a Core i7 920 between 12 and 21. i7 Turbo will report the average multiplier when this is happening.
If you enable C3/C6 and are not overclocking then the multiplier can cycle between 21 and 22 when running single threaded applications. CPU-Z won't show this correctly because it samples your multiplier once per second while the multiplier can be changing internally hundreds of times a second based on load. The less load you have, the more time your active core can use the 22X multiplier. Some single threaded apps can run 75% of the time with the 22X multiplier. i7 Turbo would report the multiplier for the core working the hardest as 21.750. The other 3 cores need to go to sleep in the C3/C6 sleep state for this to happen.
The Intel X58 board is one of the few that properly supports this feature even when overclocking the BCLK. Most don't.
CPU-Z is almost definitely correct.
Too many people blindly believing stuff like that is the reason why this issue never gets fixed.