Overclocking
Many of you must be wondering how much power a card draws once overclocked. Power consumption does not change a great deal when overclocking (just look at the many OC results in the graphs), a rough guide is to say the power consumption increases at a slightly lesser rate than the overclock. So a ~6% overclock will cause ~4% increase in power and so on. But use this only as a rough guide, and do not count on it if you are in a small power situation such as a small form factor or very small PSU. Plus this may vary with newer architectures, but should remain fairly consistent.
Eg On the HD4870X2, increasing the core clock by 50MHz causes an extra 11W at peak power draw. 6.6% increased clock speed for a 4.16% increase in power draw.
On the GTX 285 a 54MHz clock increase caused an 11W increase in power draw. 8.3% increased clocks for a 7.3% power increase.
With volt modding power draw gets insane quite quickly. See the examples I mention below for what I mean, but needless to say if you're doing any form of volt modding, make sure you have a beefy PSU that's up for the task.
Fonte, approfondimenti, charting - E' datato ma sempre valido: http://forums.atomicmpc.com.au/index.php?showtopic=264