The closer you get the more of difference you are going to notice. With a 50mm lens you are going to get minimum depth of field at 1 meter or so, beyond that depth of field increases the further you go out. The depth of field you get at 1 meter is going to be shallow, and will probably give you the effect you are looking for. I have a couple 1.2 lenses by different manufacturers, and though I like them, I find that I don't use them as much as I thought I would.
On the other hand, the 50mm focal length is not an ideal portrait lens close up. It tends to exaggerate perspective when used close, and the narrow depth of field you get so close up is more than a novelty or special-effect as opposed to something which you would use regularly. My favorite portrait lens is the 90/2. With this focal length you have a little more room to work with, your subject's features will not be exaggerated, and you can still get a somewhat narrow depth of field without being kissing distance from your subject.