MSI R4830 512MB Overclock Edition
 

I was really impressed by the overclockability of MSI's 4830. In the end I was able to get a nearly 25% overclock on the RV770 core and a 20% overclock on the GDDR3 memory. The R4830 clocks in this review were initially adjusted using CCC and then AMD GPU Clock Tool. To reach my final overclock speeds I began by increasing the core and memory clocks in 25MHz increments until I hit 710/1025. Any speed above 710MHz on the core created instability. However, the memory didn't stop at 1025MHz. I was able to get the memory up to 1075MHz before hitting any instability. As you can see in the screen shot of CCC, even with such a heavy overclock the R4830 still idled at 37 degrees.

http://www.overclockersclub.com/reviews/msi_r4830/