If your considering a Shim, you should look at the non-conductive shimms that crazypc sells. There around 9 bucks and they don't insulate heat right around the edges of the cpu. Stay away from copper shimms at all costs. I have seen an AMD fry because the shimm forced those little round spacers off the chip. Thus the shimm slid over the bridges.
Here's the Shimm link
http://www.crazypc.com/products/acce...ccessories.htm