Canon 100mm f2 vs 85mm f1.8 for portraits on 5Dc

[hiphopopotamus]

I recently slimlined my lenses (mainly due to the amount of time I actually get to do photography nowadays) to a 24-105f4 and 50mmf1.8 to try and cover most of what I want to shoot, with the 24-105 as a general walkaround and the 50mm as a portrait/low light lens, but I'm finding the 50mm too short on the 5d classic for portraits.

So I'm looking to sell the 50mm and pick up either the 85mm f1.8 or the 100m f2 instead. I've had a look through my 24-105 pictures, and the portrait lengths I usually shoot at seem to fall into the distance 80-100mm.

My immediate instinct is to go with the 100mm, but I'm worried that I might end up too close and lose the more general ability of the 50mm to perform as a low light lens. Does anybody find the 100mm too restrictive and solely head portrait focused on a full frame compared to the 85mm?

Would the 85mm be a good compromise, or would people recommend keeping the 50mm for low light and picking up the 100mm for portraits? I'd much rather to be able to just use the one lens rather than carry around both of these.

And aside from any of the reasons outlined above, are there any other reasons people here would choose one over the other?

 

[LongLensPhotography]

The difference will be absolutely minimal - I doubt you'll tell them easily apart.
50 and 85 or 100 are very different though