ATI has really done a good job with the Catalyst drivers and the implementation of the Overdrive function. While it's been around for a while, we're finding only now that people are using it more and more due to confidence levels increasing and the added function of Auto tuning when it comes to finding the maximum overclock.
Out of the box our Sapphire HD 5670 carries with it a default core clock of 775MHz and a memory clock of 1000MHz which translates to 4000MHz QDR thanks to the decision to use GDDR5 memory.
With Overdrive fired up and the Auto tune feature doing its thing, we came up with a clock rate of 840MHz on the core and 4160MHz QDR on the memory. Just shy 10MHz in both the core and memory department.
We thought that wasn't really good enough; surely an extra 10MHz could be had, and it was. This meant that we ended up with a core clock of 850MHz, a nice 75MHz up on the stock clock and a 4200MHz QDR clock on the memory which is 200MHz QDR up compared to its stock speed.