I'm 5-9 and would feel most comfortable on a 50 which has a 54.2mm effective top tube. Someone else said a 52 which has a 54.7 so 1/2 cm longer top tube. All my road bikes are a 54 top tube with 90mm stems. I could go longer in the stem, but I have no interest in being in a race stance. My wife is 5-6 and bought the 46 which has a 52.8 effective top tube. I think we have a 100 on hers so her reach would actually be pretty similar to mine.
It gets even more interesting when you go down to the 42 which is 52 effective top tube. Huge difference in seat tube to top tube, but not so much difference in top tube from the 42 to the 50.
I think the best way is to have the lbs you did your fitting done at to set their fit bike up to the 42 and 46 specifications and see if one is better than the other. They should be able to do that. Our LBS did it for us for free if we bought the frame from them and it definitely helped decide which size to get my wife.