Install 11.6 you must remove uninstall anyother versions before you install ..im not saying its gonna be a 60 frame exp.. there are some glitches ..but its playable its worth a shot
Just goto http://www.amd.com/us/Pages/AMDHomePage.aspx click on support drivers link choose your card and OS and scroll to the bottom and click Previous Drivers and choose 11.6 and download
up to an hour ago i couldnt play at all ...just try it ...PLEASE REPORT BACK IF IT WORKED FOR ANY OF YOU FOLKS

Does it fix the very annoying tearing and texture pop-ins?

no its buggy color off in areas ....just reduce your resolution and play.....this is a ATI failure not id softwares fault ...hey im killen in window mode

I'm hoping I don't have to go that route. My brother is using the exact same 5850 as I am and the AMD Rage patch fixed every problem he had. I'm still having every problem (textures, freezing, stuttering, you name it). I hate going downstairs now (he's playing it as we speak), haha...