My 4870 only runing at 850/1100 from 750/900 on a simple after market air cooler.
It's all about cooling, and luck of silicone.
It works the same for all cards, if you go too far, you can lock up the PC.
Although I have found with my Ati card, that VPU saves a lot of restarts.
Normaly taking the memory too far out of spec, willl result is a lock up that VPU cannot recover from. But VPU works well with core overclocks and/or overheating.
Good warning though, should go to Nvidia users too.
If you do not know what you are doing , leave well alone.
4800 OC> http://www.xtremesystems.org/forums/...d.php?t=193707
Overdrive the overclocking feature you mention is in 9.2 CCC, has been aroud a while, 9700 was the first card to feature it IIRC in CCC 3.8.