At 4.2GHz you should be able to overclock by ONLY adjusting the frequency (may have to do each core depending on BIOS).
This keeps the Intel Power Management at optimal and the temperature down. I overclocked to 4.4GHz but to keep it stable I had to make a bunch of changes that raised the temperature by 20degC (under maximum heat stress test in Prime95. Went from 68degC to 88degC). That seems hot but it was hot here in my room. The point is the DIFFERENCE in temperature.
1) I agree that cooler should be fine.
2) Install the motherboard software to control the fan and setup a profile (say 50% fan speed in idle and ramp up as it gets hotter).
3) CPU to 4.2GHz
4) Adjust RAM if it's not optimal (can change when messing with XMP etc to adjust CPU)
5) Finally, test the CPU with Prime95 and the RAM with MEMTEST or Windows memory diagnostic.
*If you ever have fan noise problems, you can easily replace it with a compatible fan. You'd want a 12cm, PWM fan with 500RPM to 1800RPM profile I believe (or roughly that RPM variation).