I didn't start where you did, so I'm not sure how helpful my thoughts will be, but here goes.
I started with measurements of
34 (underbust)
32 (waist)
39 (lower waist/jelly donut)
44 (hips)
And I've managed to lose 16.5 inches total so far. My last inch has just come off my lower waist in the past week or so (not typical for me at all).
My most difficult area has been the lower waist I'd say (where the slightly sticky-outie tummy bit is) and it took me almost 30 pounds to lose 3.5 inches in that area. I'm not too far from my goal now, and I'm still losing weight in my most problematic areas (donut and hips areas), but I'm also not expecting to try and lose a lot of inches in the next 15 pounds or so.
I'd say based on that, you might be able to get to a 28 inch waist, but it does depend on your body and how cooperative it is, as well as your natural body type.
Don't know if that was any help at all, but might give you a bit of a starting point.