To overclock the Viper V770s I put a 50mm fan on top of the heatsink and some PCI strips on the memory chips. Since both card are the same except for memory, they should overclock to the same amount. It turns out that the 32 meg Viper can have its memory overclocked higher than the 16 meg Viper. The 16 meg Viper can have its core overclocked higher than the 32 meg version.