I don't even see the point of comparing overclocking between brands. Surely if a card can't overclock much even if it's staying within it's thermal limits, then you're getting nearly the max possible out of the card, which is good, right? Who wants to buy a card that leaves tons of performance on the table for which you have to mess with voltages and careful tuning?
Comparing overclocking ability is even worse than comparing clockspeeds between brands. It doesn't tell you how much work each card is doing per clock, so a slower clocked card could have higher performance.
How is any of this even useful unless your only aim is to see how far above stock speeds you can get the card, ignoring if one is already most of the way there already?
I do, because i know how to bring out that performance. And i can do it for much cheaper than just getting a 780ti. Beating most 780tis in the process.