Stable OC has more to do with the CPU than the cooler. The cooler simply keeps it below its thermal maximum.
For example my 955 has plenty of thermal headroom, but from 1.4v to 1.5v it doesn't get stable past 3.9 GHz. But my temps are still fine.
To overclock the i5-750 you have to adjust the BCLK which in-turn changes other frequencies. In which case you have to adjust their multipliers to keep them close to their stock speeds(generally) If my memory serves me right there is some multiplier changes you can make to the actual CPU but it's very limited(like going from 21x to 22x)
I think there is an Intel overclocking guide in the overclocking section.