I have a '99 528i sport. I currently have 18" M-Pars on there and I have the original 17" style 5's in the garage with 235/45 17's on them. I'm wondering if it would be ok to go with 235/55 17's on these wheels or would they be too tall? Any help is appreciated.

I don't see why you would want to. That high of a profile would really throw off the handling and speedo and possibly rub (I doubt it).