OK, so there is several different options you can tweak.
First, of course, is loadline calibration. Loadline calibration is an effort to keep voltages constant, by providing more current, as the votlage drops based on how much current the CPU consumes.
As you increase CPU frequency, the amount of current used by the CPU to switch states increases(which is why temps increase with speed, even though volts may stay the same).
The VRM charges the capacitors at a set frequency. if we increase the frequency that they are charged, the VRM can supply more current, and the cpu can use more before voltage fluctuations are noticed. If the frequency between the VRM and the CPU doesn't mesh well, it can cause stability issues.
You also have the option of customizing the VRM so that the phases are either all always on, or they are enabled dynamically based on load. When it is set dynamically, the time between phases going from off to on states may lead to teh VRM not supplying enough for a fraction of a second, which may be enough to break stability.
Because it deals more with how much power the CPU comsumes, there really isn't real specific adjustments I can suggest, as it will vary from CPU to CPU, as the VRM does react a bit differently with each of the CPUs I have on hand here.
I look at it this way...the voltage you give is the wave the current rides to the CPU. Instability is rocks that make the wave crash, and not continue, so we must adjust the wave's form so that it go over the rocks. Depending on how far from the coast(stock) the waves must go, they might need to be taller, or they might need to be more often, or they might need more force. In the past, we've only had very little options to make the wave go farther...increasing the wave height(voltage), and the wave force(current), but the frequency, in most products, is not something we could adjust.
I apply this to my overclocking in the reviews, and try to use the same wave, 1.27v, to see how far, with that wave, things will go. If the VRM supplies more current, the wave goes farther, but at the same time it gives each board the same wave to work with, and the same rocks(the CPUs stock), so really isolates what's going on in the VRM. Hence the VRM power comsumption numbers in my reviews.
The parts in the VRM usually dictate the frequency of the VRM, but guys that use extreme cold have found that the higher frequency can allow for the CPU to go further. To me, this is why certain products have huge followings for extreme clocks...of course, it's not quite exactly os simple, but I think you get the point.
So you need to play with it...finesse it...settings that are too high may only offer additional heat, so of course, you can just push everything to the max, but you'll also have the extra heat to deal with.
If your votlage is not stable, of course, some of those waves may hit rocks, so the main thing to try, IMHO, is stabilizing that wave. The votlage SHOULD vary a bit under load, as that is the nature of the circuit, but not too much, or the wave behind will not reach as high, and stability may falter.
Of course, this is all very abstract...but if voltage is fairly constant, than you may want to look and increasing the VRM frequency, but really, error codes and how the system crashes should point you in the right direction. Maybe the CPU has too much heat, maybe the voltage needs to be higher, maybe it needs more current...
Over the next several weeks while working between reviews, I'll be posting more info specific to each board, and overclocking, and what I run into for issues, and how I overcame them, so perhaps we can take that journey together.
I have a review to finish right now, but will be done later today, so look for my posts this weekend, as the ASUS is the board I will be looking at this weekend, and perhaps I'll have better, more direct, info for ya.
some time in the future. 
Will have to get used to it I guess.
