Don't use 2.2, bugs and low performance. SDK 2.1 or even 2.4 would be better. I have 3 Xtreme 5850s and they all mine at around 358~ with a modest overclock (900 core, 300 mem)
 
Here's what you want to do:

1...

6. Set core to 900, memory to 1200 (300x4), and voltage to 1100
OPTIONAL: Set fan speed to 100%

Enjoy high GHashes at 50°C~!