alot of people overclock for gamign because they think it will make a difference, they are generally mistaken.
Overclocking is great for very cpu intensive tasks, this could be 3D rendering, games such as FSX where there is a lot of scenery to load (this is one of the only games that really needs masses of cpu power).
i dunno about 3D i dont have it, I overclock because I do a lot of mathematics priocessing, matlab work, 3D modelling, games design, all of which benefit from overclocking, it just happens I polay games too.