Having used a few 7xxx cards Greg i can confirm these rough Asic guides to be correct in terms of power usage, voltage level and voltage level based on the type of cooling you have.
A high asic card is much more suited to an air cooler as the default voltage is much lower so temps will be lower giving your more room to work with before you trigger the heat limits of the card restricting an overclock.
The most important factor is luck in the silicone of course, but to say that Asic means nothing i cannot agree with.
You could have a good clocking card but if its a low Asic card you'll never reach its potential with a high default voltage and a stock air cooler.
If you know different, then feel free to contribute something.