I think it is very likely that at your height and weight, if you lost 17 lbs you would be a size smaller. Of course, sizes aren't consistent and different cuts are appropriate for different shapes, so for a given selection you can't predict what size will fit best.

If you are interested in dropping inches, exercise works very well (for me, at any rate). It seems to do a better job of reshaping than just losing weight.

I drop a size after about 15 pounds loss.