How to overclock hd 5750

This is perfectly safe as long as you use the software and are careful with the overvoltage. What's more, if you talk to your local Asus support team, you may find that the card is covered by warranty if you are using their version of Smart Doctor for the O/C.

Having said that, not all cards/PCBs/processors are created equal, and it may be that you encounter problems. Find out about warranty first if you can't afford to replace graphics card, but keep the voltage below 1.25 and only oc when you want the extra power and you should be fine.