Just for your information, the IHS is made of zinc plated copper.
as for overclocking with ATITOOL, i would recomend the folowing:
1 ) Start ATITool and click the "Settings" button in the lower right hand corner
2 ) Select "Artifact Scanning" fron the drop down menu at the top
3 ) Check the "Stop scanning for maximum clock after ---- seconds without artifacts" box
4 ) Enter 7200 for the number of seconds
5 ) Click the "Back" button in the lower right hand corner
6 ) Click the "Find Max Core" button and then find something to do for the next 2&1/2 hours
7 ) After 7200 seconds of stable clock speed a dialog box will appear to inform you of the max stable core speed. Click "OK"
8 ) Click the "Find Max Mem" button and then find something to do for the next 2&1/2 hours
(It will warn you about overclocking the mem when the core is overclocked - just click past this)
9 ) You'll see the dialog box again, this time with your optimal core and mem speeds! Click "OK"
10 ) In the "Profile" section at the top, click "New"
11 ) Name this speed profile whatever you want then click "OK"
Hope this helps