Factotum: You might be having a problem with Turbo throttling at full load. That's when your +1 Turbo will rapidly cycle on and off so your CPU multiplier will bounce back and forth from 21 to 20. That is likely why RealTemp is reporting 20.8 for your multiplier.

Try running i7 Turbo and keep an eye on what it shows for the Calculated Multiplier. Run Prime 95 Small FFTs and see if it is steady at 21.000 or not.
http://www.fileden.com/files/2008/3/3/1794507/Turbo.zip

If your Turbo is cutting out at full load then there should be an option in your bios to turn this off.