My card also has massive graphics corruption in DOS. My startup splash screen is unreadable and when I flash it makes all that mess you saw. My card has never been detected as PE and I never cared. Being detected as a PE is meaningless. You must also do all your overclocking in ATITOOL now. The problem you have is that ATITOOL is reading your 2D clocks. These cards run 2D and 3D modes. You will certainly need to raise the voltage on the GPU to run 3D. I am not exactly sure what you will need to raise it to, but for me my card runs 1.25V in 2D and 1.4V in 3D. 1.4V gets me a nice mild OC and your card will probably clock better with lower voltage than mine. Make certain you save your new profile. Also, be sure to do this. Click Properties. Make sure the box for Clock Speeds AND Voltage are checked as well as Fan settings.
After you find a good voltage/clock setting, you need to do this. In ATITOOL, click Settings>Startup and set it to load on Windows Startup via Registry Key. This will enable it when you start up without you having to manually do it every time. Now, click Settings>3D-Detection. Under "When 3D application is detected" check off Load Profile and make sure it is listing your custon profile you created. Under "When 3D application is closed" check load profile and set it to default. That will put it in 2D mode automatically.
I don't know what cooler you run, but the stock cooler kicks ass, it is just LOUD!!!!!!! I set my fan to run 60% all the time and it is a good setting for sound VS cooling. My idle temps stay around 40C and it loads around 60C. These cards are good for 80C+ so I am happy with it myself.