Hey Timetraveller, personally I went for the HDMI option. My reasoning for that was due to the fact that the output through HDMI/3G isn’t ‘clean’ meaning you cant use the output to record to an atomos or similar, and both only output a max of 1080p (no 4k). In terms of monitoring, there are 2x HDMI’s in which I’ll mainly only use one monitor mounted with the camera. Then when it comes to it, there are plenty of ‘wireless HDMI’ options if your shooting something in which the director would like to have a separate monitor.
IMO I don’t see any reason for more monitors, but everyone works differently. Personally I think its more for preference.
You might want to take a look at this: http://churchm.ag/hdmi-vs-hd-sdi/
Though I feel most of the points made in that article are kind of redundant now (especially for monitoring purposes). Such as the part about SDI being able to lock in place, you can now also buy ‘locking’ hdmi cables that will do a good job.
Hope that helped!