You have a pretty good understanding of the lenses and how they function. In order to get good bokeh one must control the depth of field fairly tightly. The Nikkor 85mm lenses do a great job for that on the FX format cameras. The same lens will function as a longer focal length lens on a DX format camera. Depth of field is also affected by the aperature setting. If you are purchasing an FX lens to use on a DX camera you will probably want a shorter focal lentgh lens like the 55 mm you mentioned. Below is a very good summary of depth of field that I picked up somewhere on the Internet. I am sorry I cannot properly credit the author but the information is very good. Lastly, take your camera to a local camera shop and ask to test one or more lenses. Virtually any good camera store will allow you to do this and you can see for yourself what kind of bokeh you are getting at various distances using different aperatures.

Depth of Field (DOF) rules of thumb:
1. As the aperture gets larger the DOF get shorter. The inverse is true as the aperture gets smaller the DOF gets larger.
2. As focal length gets longer the DOF get shorter. The inverse is true as the focal length gets get shorter the DOF gets larger.
3. As the sensor/film format gets larger the DOF get shorter. The inverse is true as the sensor/film format gets smaller the DOF gets larger.
4. As the distance to the object gets shorter the DOF get shorter. The inverse is true as the distance to the object gets farther the DOF gets larger.