Overclocking a graphics card today is simpler and safer than ever, and with a bit of tuning you can extend the life of an aging graphics card or get even better performance out of a new one. But what if you don't have just one graphics card? What if you have two, or three, or even four running in SLI? How does that affect the overclocking process? PC Gamer chats to NVIDIA's Tom Petersen to find out.