I say do video first, because OC'ing your CPU and RAM is a more percise and time consuiming job. Heck with your video card if you want to do it fast and easy get something like ATI tools (or the Nvidia equivilant) and run the auto overclock feature, it will find your max memory and core speed pretty fast while all the while checking for artifacting so you know it's stable. Your CPU and RAM are a different story so I'd do them second cause that takes more of your time and attention and it's nice to get one thing outa the way before moving on to the second.