Cooling is great. My case temp never goes above the ambient temp. I'd recommend adding a 120mm fan to the middle drive cage to push some cool air over the vid cards. The fan bracket is included and it fit perfectly with my reference-sized 4850. Even if it doesn't fit, you can remove the middle drive cage and attach the fan directly to the front. I used one of these:
The Antec P182 is a great case. With the power supply mounting at the bottom, you'll have room for the longer PS. Running cables on that case is great as well - hide them all behind the motherboard, with many openings to get them to the drives and cards.