If, like me, you are a novice at overclocking, and want to try to overcome the limits built into the 5850's BIOS, here's a very handy page showing the different ways you can do it, with links to all needed programs:
http://tech.icrontic.com/articles/overclocking-the-radeon-hd-5850/
http://tech.icrontic.com/articles/overclocking-the-radeon-hd-5850/