Mintmaster said:QFT.
What does 10-20% do for you anyway? I'd rather lower the voltage and spin down the fan. For video cards, you need 60% to get an extra resolution, and even then only if you're not CPU limited. 15% is meaningless except for benchmark wars. I wouldn't upgrade my video card unless it's a factor of 3 or 4 at least.
Something ridiculous like an dual core Opteron going from 1.8Ghz to 2.8GHz is a different story, though.
Running my a64 at 2.2ghz instead of 1.8 ghz provides a very noticeable speed increase, and it still runs quite cool on stock cooling, my motherboard doesn't even allow me to change the voltage