For 645, I think that the 110mm is a bit short for head/shoulders portraiture. At 2m distance, the image field with the 150mm is 50cm x 70 cm. With the 110mm, you'll have to get closer to 1.5m for the same image and risk a "big nose look". For tighter head/shoulders portraits, the 210mm would be better. At 2m, the image field for the 210mm would be 40 x 50 cm. So it depends on how much space around the head/shoulders you want in your photo.
The 105-210mm zoom is a versatile portrait lens although I found it a bit heavy. The A 150mm f/2.8 lens is also really nice. I'll see if I can post an example image from that lens tonight.