To overclock today we are using Sapphire's TriXX software tool, which has worked well for us in the past.
The Sapphire HD7770 GHZ FleX Edition ships with a reasonable amount of headroom on both core and memory. We managed around a 10-11% increase on both memory and core clock speeds. Good results.
The additional, manual clock increase manages to push the score to almost 4,000 points. Not a huge increase, but enough to generate another 1-2 frames per second in many of the engines we tested today.
Another good card from Sapphire. nice n quiet too.
Good value for money, not really a gaming card, but good for a workstation IMO