I prefer PowerStrip, it has many more functions than just to oc the gfx-card.
I like the option to force a specifc refresh rate with a given resolution a lot for example, this way when I run the games in 1024x768 it forces 100hz (instead of defualt (60hz) because it's another resolution than my desktop (1280x1024)) which is mich nicer to look at.
But it's great for oc'ing, I use it to runh my Ti200 at 230/530.