PNY are good simply because they are memory manufacturers as well so you can guarantee that their cards will have good DDR memory on board. If you look back at previous benchmark tests you will see that Asus is very often top of the pile both in scores and in prices / packaging.
I think that as a general rule the most expensive card will have the highest score with a slight variance of course. Then as you get cheaper the packaging varies as does the clock speeds and build quality of heatsink / fans etc...
Same as CPUs really - most expensive = most powerful. There are exceptions where some manufacturers charge more for their brand rather than the raw card speed but then there are others that will be cheap and powerful but maybe at the cost of a loud fan (Geforce FX anyone).
4.77MHz to 4.0GHz in 10 years. Imagine the space year 2020