As far as there being a difference, I really don't know- but, I believe mine are 5.5", however, the original owner may have changed the wheels, so I'm not the best one to ask.
I'm not the man like Zen is when it comes to knowing what the heck I'm talking about. If you are considering getting new wheels like I am, and you have the originals on the car, you can usually just tell the person you are buying wheels from what year bug you have and they can tell you what size you need.
My mechanic has been working on VW's since the late 60's, and I usually order what I need through him, since he has a better knowledge of VW's. I am ordering my EMPI 8 spokes through him, and he just knows what size to get. Any reputable tire/wheel store should know exactly what to get for you.