I have both the 70-200/4 IS and original 70-200/2.8 IS... as well as 85/1.8 and 135/2.
Trust me... For portraiture, keep your 85/1.8 and add the 135/2L! On your 5DII both are superb portrait lenses. For portraiture, the zooms will not be better in any way and give you less control over depth of field (are f2.8 at best). The "Canon white" zooms are larger, heavier to hold for long sessions, and more intimidating to non-professional subjects, too. The only real advantage the zooms bring is the convenience of not having to move yourself, to get the composition your want. I use them for sports, but generally not for portraiture.
I happily used 50/1.4 (left) and 85/1.8 (right) for portraits on crop cameras for years...


I still use both those lenses on both crop and full frame cameras. But the day I ordered my 5D Mark II (almost four years ago), I also ordered the 135/2L. I knew I'd want it for portraits, having used 135mm lenses a lot when I was shooting film back in the good/bad old days. If I were buying the camera again today, I'd do exactly the same.
You haven't really experienced a Canon portrait lens until you get the 135/2 for use on your full frame camera. The problem is, if all you shoot is portraits, after using the 135/2L for a little while, you might find yourself wanting an 85/1.2L II and a 50/1.2L! It can be an expensive addiction.
The 135/2 works very well with a quality 1.4X teleconverter, too, for an effective 189mm f2.8. If interested in that, I'd recommend the Canon 1.4X II or III, Kenko DG or DGX "Pro 300" 1.4X (and have recently heard really good things about the cheaper Kenko MC4 DGX 1.4X too, but haven't had a chance to try one yet). I've used it particularly with the Canon 1.4X II and notice minimal loss of IQ or AF speed. I would expect IQ from the Kenkos to hold up, but there might be some drop in AF speed.
Sure, I occasionally use a 70-200 for portraiture and it works pretty well..
But I'd rather use the 135/2 much of the time, when I don't need the convenience of the zoom. The "portrait" below of my cat was likely the very first shot I ever took with the 135L (she often was the subject of any new gear and like to help unpack things)... This was on my 5DII, wide open at f2.0 abd near the lens' minimum focus distance, with the camera at ISO 6400 and 1/200 shutter, handheld...
Here's the 135/2 on 5DII at a greater distance and f4...
On a crop camera, the 135/2 is sort of like a "poor man's" 200/2L (without the IS of course), here on 7D at f5....
And, yeah, the 300/4 IS is an interesting portrait lens... but you'll need a lot of working distance with it!
Heck, a 500/4 IS with a 1.4X on it can be a portrait lens too... even more working distance needed.