Speaking from experience, a Q6600 should easily run at 3.0 GHz with little or no voltage increase with the stock cooler. To go any higher will take better cooling.
I am guessing that you have a Gigabyte motherboard and you actually mean "M.I.T." and not "M.T.I".
This should be your first stop.
Core2 Overclocking Guide (our generic guide)
http://www.tomshardware.co.uk/forum/259899-11-core-overclocking-guide
Shadow's Gigabyte motherboard OC guide:
http://www.tomshardware.co.uk/forum/page-245679_11_0.html
It's for an EP35-DS3L but all the Gigabyte Core2 BIOS's are similar.
Go through the guides. Then take your core voltage off Auto and set your memory voltage to factory recommended values. Change the System Memory Multiplier from AUTO to 2.00, 2.00B, or 2.00D - whichever you need to set the Memory Frequency to twice the FSB. At an FSB of 266 MHz, your memory clock should be at 533 MHz.
Download CPU-Z to check your FSB:RAM ratio. It should be a 1:1 ratio.
I think you are inadvertently overclocking your memory. With your memory settings on Auto and the FSB freq set to 333 MHz, your memory is actually running at (333/266)*800 or DDR2-1000 speeds.