The Asus HD5750 is supplied at 700mhz core clocks with memory at an effective 4.6ghz. We handled overclocking with the fan set to auto to keep noise to a minimum and found that we were able to squeeze considerably more from the board before errors started to occur.
The final figures we settled on were 840 mhz on the core and 1270mhz on the memory. As always with overclocking the results will vary from card to card but this shows a large amount of overhead and we would assume most cards would reach 800 core and 1250 memory easily enough. Figures worth taking into consideration if your game is currently just slightly juddery at the given settings.
We also overclocked our reference HD5750 and achieved 840mhz on the core and 1280mhz on the memory, slightly higher than the Asus board achieved.