Another thing to consider: The Sigma 70mm EX Macro is BRUTALLY sharp, and I don't mean that in any negative way. However, if portraiture is your prime focus (!), you should probably invest as well in a softening filter or some PP time. It does not look very flattering on some subjects. Head shots, even at F4.0 will reveal absolutely every skin features, desirable or not..
However, for macro use, this is the sharpest lens I have ever used. Brutal!
On the other hand, FA50, DA70ltd, FA77ltd will allow you to use on-board CA and distortion correction (K-x and K-7), if that is important to you.
I still use mostly my trusty FA50 and FA77 for shoulder & head shots.
Hope this helps
Gene