I had a .73 carat princess cut diamond. It was polished to .69 and I could tell the difference. The experts would have to weigh in because I bet it really depends on the stone and the situation. I am confused if it has the same table and depth, then it probably wouldn't be noticeable. Just my two cents.
I think at least if side by side the difference would be noticeable. I suspect that the % difference of the sizes will determine whether a difference can be noticed. In this case the larger is 8% bigger than the smaller one. On the other hand, a 1.72 ct vs 1.78 probably would not be distinguishable. Just a thought.