Another point you may want to consider is noise. Some of us need to live with our GPUs and, in such situations, noise often gets the spotlight. It is often something that people don't consider until they turn on their shiny new mining rig.
For example, I picked up a couple of plain vanilla Asus 5870s a while back. They were both very quiet (as most 5870s are) at idle, but once you started mining the fans (on auto) would go ballistic. They both sounded like a vacuum cleaner. Setting the fan speed manually didn't help; at lower speeds the cards would go near 90 degrees. It is possible that both were defective in some way, but more likely it is a characteristic of that particular model.
So I swapped those with a pair of stock Sapphire 5870s. Standard stock blower fan. The Sapphires were fine; mining with auto fan is relatively quiet with those. Well, 'quiet' relative to the Asus.
I also have some Gigabyte 5870s, the models with the dual fan. I find them to be very quiet as well on auto fan.
One thing you can do (though it is an additional expense) is to replace the stock cooler with a 3rd party heatsink/fan. I've used a couple of Arctic Cooling Accelero Twin Turbo Pro ... I find their tolerances to be hit and miss, so I avoid those now. I've had great success with the Zalman VF3000A; those are very quiet and efficient coolers. You can also do water cooling, but don't jump into that unless you take a hard look at expense vs payback.