ohmychonny :
I also want to OC my g3258 to 4.2ghz, were you able to do so? Was the temps ok with the stock fan? Did you adjust the voltage, if so what was a stable voltage.
I once clocked it up to 4.2 GHz, but only very briefly. Idle temps were about 40C range (memory is kind of vague) and within 30 seconds of starting a stress test, it crashed. It was hitting almost 90C. I think it was at 1.2 volts, but I really don't remember. Obviously, way too hot and 4.2 was too much.
I'm not much of an overclocker, so most of the time I just left it at 3.8 GHz, but I got it to run stably at 4 GHz and go through stress tests. Again, voltage I believe was 1.2. Idle temps were about 38-40C and it sometimes spiked up to 80 C in stress tests. Not recommended, but for a $60 CPU and a stock cooler, it is was a respectable performance bump!
Since then, I dumped the G3258 for an i5-4590 just so I have the four cores for 'future-proofing,' so I can't help you by testing more.
Remember in all of these, I am very inexperienced with overclocking, and I could have been doing something wrong. If you have a real Z97/Z87 motherboard, or if you do more research than me, I'm sure you can find some tips and ways to overclock to run it cooler at higher frequencies. Heck,
i'd start my own thread just asking for tips on the G3258!