The 2s are quite a bit different from the 2.8s. The focal lengths are similar, but that's about it. I got to play with one and it what it does with colors really needs to be seen to be appreciated. I was inches from buying it but basically for me it would be a really expensive toy for amazing street photography. This lens is for creating "art."
I do some portraits, but they are almost always outside and involve lots of movement. I can see using this in studio without autofocus, but I don't trust myself or the patience of my clients to use it regularly. Additionally, at f2 with three or four flash setup outside, I'm going to need at least a three stop ND and it's tough to manually focus when the viewfinder is darkened. I can't imagine trying to focus it with a 6 stop ND.
That all being said, I wish I had bought it.