How much does overclocking affect power consumption?

[Schneizel]

Say I have a build with a 2-Way R9 290X Crossfire that loads at 650w with everything stock.If I push literally everything to it's limit, how much would that wattage increase?Would it go up to 700w?750w?

 

[menetlaus]

You could push that configuration well over 1000W or beyond (with high overvoltages and the right cooling setup).

Question becomes how long do you want it to live and how much to spend on the cooling setup?

The hotter something runs - the shorter the lifespan.
The higher you overclock (and overvolt) something - the hotter it runs.
The more you overvolt something - the higher it will overclock (up to a point).

Overclocking is all about the tradeoffs for available headroom on the parts, available power, and heat. So without some additional info on the case, cooling, desired lifespan, CPU and much more - we can't really answer what the "limit" is for wattage it can draw.

 

[Schneizel]

How quickly does it scale though?How much would it take for it to hit that high assuming both are average cards?