I would advise never wearing the five-button vest with a PC. And that scrunchy thing, well it's just not even worth discussing.

I almost always agree with Jock, MoR, and JSFMACLJR. But I must say that I do not care for the beltless look if there is no waistcoat. I think I have only worn a PC sans waistcoat one time, and I had a black belt with sllver waist plate at the time; it was mostly due to hot weather, as I recall, and I kind of like the look even though I rarely emply it. (Heavy emphasis on "kind of" since I am not completely sold on it.)

And the PC with belt but no waistcoat seems to be a very clean look. A starched white shirt is part of the overall balck tie look, I think, and both the belt and three-button waistcoat allow it to be seen. So, stick with the basics and tradition and you'll always be thought well-dressed. As Jock pointed out, the differences are quite minor.