I haven't got my car running yet but I am planning on running either 17 or 18 rims. So I can't really tell you what the difference is in comparison to an E-body.
I know one of the main reasons for going that route is handling. The idea is that with a smaller side wall, you gain rigidity in the tire, thus increasing response. The down side is that your ride will typically be harsher because you do not have as much cushion or flex to absorb bumps. The other part of this is comes into play with the width of the tire. A wider tire will usually have a smoother ride because your tire doesn't fall into the holes and divots in the road. The down side to that though, is that your tires will want to track the ruts in the road. The tighter the suspension (good for handling) the worse the tracking becomes. If you have good roads where you live, this won't be much of an issue for you. I have noticed it really bad here in Missouri when I had my Z06. Some roads can be very tiresome to fight.
Personally, I like to feel the road and don't mind a little jarring once and a while.
I hate the feeling of floating on the water that some cars have.
