In benchmarks I've seen, rev. 2 (the bottom one) actually runs cooler, and quieter even maybe. They do put air in your case, so if you did get Rev. 2, you need great case airflow. I'm also not sure rev. 2 has voltage control if you're interested in overclocking.
EDIT: Oh, here ya go: http://www.anandtech.com/show/3596
Take this with a grain of salt, these are 5770's but it's the same style coolers.