Up to you if you can see any difference with the photos taken.
Think over things like working distance as well. Even though 100/2.8 is macro, which means you can focus nearer than the 85/1.8, you still need a certain distance to get specific coverage of subjects (eg. head shots : 1.2m (85mm) vs 1.5m (100mm), etc).
Size, weight, portability?
Another is focus speed on a macro lens vs normal lens.
Do you find them to have the same DOF or rather do they produce comparable OOF areas for subject isolation for the same sized subject on the photo?