it's like any fast lens on the A7r. Some people dig it, some cant use it, but in either case, it's considerably better than any DSLR. For instance, swimming: when I focus peak, I can see the focal plane, so when my kids I can follow my kids with the focal plane when they are completely submerged. It's actually quite easy when you get the hang of it.
I was shooting kids playing a large group running game this weekend (135F2) and it was a breeze tracking them. For portraits that are real tight, I may tap the zoom in to get the eyes in focus, but for full body, I set the peaking high enough so that the eyes twinkle when in focus. From what I recall of my friends D800 that live view was pretty terrible, so the A7x camera will be night and day.
the EVF will take a lot of patience to get used to, but after a year of use, I finally let go of canon DSLRs. I also shoot a lot of events, as I'm an event photographer for my kid's school, and I find that I technically dont need AF. I do bring some native glass to events, more for security, but lately, I've been leaving them home. My preferred everyday kit is like a 50/100 or 135F2 combo. I use the 100/135 often simply because the 200 can get awkward at times, and the 135 is pretty close to *look* of the 200. For a formal event (like weddings or christenings), I'll pull it out, but for performances, recognition ceremonies, not always. That's where the 135 comes to play. I do have a few 135's currently, the FD 135F2 and EF 135L. No question, the 135L is better, it has ED glass similar to the 200/2. Amazing lens, however a tad too large on the sony, which makes me opt for the FD 135F2. It has more CA in some instances, but it's a damn amazing lens in it's own right. I've played with 5 or so 135's and hard to find a bad one.
as for specific body, I'de get either the A7ii or A7rii if I were you. The IBIS turns the 200/2 into a 200/2 VR , very
135 into 135IS.... damn amazing when shooting low light, which I do often.
IBIS is more important than the resolution, when I shoot events or handheld. I will shoot the 200/2 handheld, in fact, I do most of the time. The next time I will bring it out will likely be the christmas program, hopefully I'll have the A7rii by then. The IBIS body is a gamechanger for me. So much better consistency, and totally opens up the 85/100/135/200 for low light photography.
Sony A7rii/A7riii - FE 12-24/4 - FE 24-240 - FE 28/2 - FE 35/2.8 - FE 50/1.8 - FE 85/1.8 - EF 135/1.8 Art - F 600/5.6 - CZ 35-70, 100-300 - Astro Rok 14/2.8, 24/1.4 - Tamron 28-75 f2.8, 70-200 f2.8 VC