It's pretty simple really- go into the BIOS, set the multiplier to the desired frequency (make sure BCLK is 100 MHz) so set a 45 multi for 4.5 GHz etc. Then leave voltage on auto with automatic offset (just to see what it uses automatically). Turn LLC (load line calibration) up to 75 or 100%. This helps to minimise Vdroop (when the voltage dips below the desired amount when under max load). If it droops too much, it can cause instability, hence we use load line calibration to avoid this. One some cheap motherboards, using high levels of LLC can cause voltage spikes when the CPU goes from max load to idle as it can't respond to the sudden change in load fast enough. This shouldn't really be an issue with a sabertooth board, as it is a good quality motherboard.
Then boot into windows and see what Vcore it uses under load (use a stress tester like IBT or Prime95). If it is unstable after a few runs of IBT (I use Intel Burn Test just to quickly check initial stability before doing 8 hour runs of Prime95 when settling on my final 24/7 overclock), then set a positive offset (this will increase the idle and load voltages that the motherboard would have automatically used at that frequency). Bump it up in small increments until you reach stability.
If it is stable automatically, try a negative offset (does the opposite effectively) until it is unstable. When it is unstable, back off the negative offset until you reach stability again. Once you have found the lowest voltage to maintain stability at your desired overclock, then do around 8 hours of Prime95 small FFTs. If it is stable, then great! If it is unstable, then increase the voltage (by reducing/increasing the negative/positive offset respectively).
Some people just use a fixed voltage (which is easier as it makes setting the voltage level easier) but idle temps and power consumption are better if you use offset voltage (which allows the Vcore to drop when frequency and load drop).
4.2 should be attainable on stock voltage (mine is at 4.2 as well). For 4.2 GHz, my 3570k uses 1.16v at full load (and 1.18v max voltage- the load voltage is lower due to Vdroop), and 0.944v at idle. This is with a negative offset of 0.05v (ie, the motherboard would automatically used 0.05v more if I hadn't changed the offset level). However, remember that every chip (even if you have a 3570k as well) will require slightly different settings- you may have a really good chip that can do 4.2 GHz fully stable on only 1.1v, or you may have a not so good chip that needs 1.2v to be stable at 4.2. It is what's known as the silicone lottery, the same is true for GPUs on graphics cards.
Also, remember the idea is to get the highest overclock at the lowest voltage (since using a higher voltage increases power consumption and heat). The higher the overclock, the more Vcore is required in order to maintain stability. Generally, motherboards tend to automatically overdo the required voltage with small overclocks (so use a negative offset to reduce this voltage level) and underdo the voltage with high overclocks (they don't supply enough voltage to maintain stability at the chosen clock speed, so you need to use a positive offset to get stability).
I hope this kind of helps, I'm not exactly an expert on guides so I would suggest looking at some better written instructions as well. Good luck overclocking, it's what this forum is all about after all
