You can actually Disable the setting responsible for changing the clock speed of the CPU.
Using this Guide:
Core2Duo Overclocking Guide v1.1
you can get the most out of a CPU by doing the following:
1. Disable ‘AI Tuning’ for ASUS, ‘C.I.A.2’ for Gigabyte
2. Set PCI Express (PCIe) frequency @100Mhz (‘Auto’ for DS3/DS4/DQ6)
3. Set PCI frequency @33Mhz
4. Disable Hyperpath 3 (for P5W DH only)
5. Disable any ‘spread spectrum’
6. Disable Q-Fan (for ASUS only)
7. Disable ‘Limit CPUID Max to 3’
8. Disable any overvoltage protection
9. Disable ‘C1E’
10. Disable ‘EIST’
11. Disable Virtualization Technology
12. Disable No-Execute Memory Protect
13. Disable any other thing you don’t use
14. Do not enable any speed enhancements you see
I believe the EIST and C1E settings are most relevant to the changing Proc speed during different types of load..
Disabling them would mean the CPU will always run at set clock speed. Which for that Proc is 8 X 266.25, I think.
Thats only part of the guide.
I suggest you follow it from start to finish.