Sparkle guarantees no more than 1% variation from where the voltage is. Example: if your 5v line is 5.2, it will not vary more than 1% from there. It could be as much as 5% one way or the other but will not vary more than 1% from there(5.2). The PCPower and Cooling I believe keeps it's voltage within 1% period. You won't find a PC Power and Cooling at 11.7 on the 12v rail but 11.7 is only 2.5% low and atx spec has a tolerance of 5%, and 5% is really fine unless maybe you are a hardcore overclocker. The stability of each line is what you want from you PSU. If a PSU is over by .2 volts that means nothing. A PSU which is .2 under and has low ripple is far better. Most people seem to be overly concerned about being a couple percent off and that's just the tip of the iceberg when you look at all the other components and how they are designed. Hope this is easy to understand.