assuming that you can use PoE, why would you use SDI? PoE seems so much more convenient and does everything in one cable doesn't it?
the price difference between 12x, 20x and 30x zoom is fairly small. Assuming that it is negligible in your budget, why would you ever choose a 12 or 20x zoom over a 30x? (Yes the field of vision is slightly wider in the 12x, but is this very noticeable in practice?
Using SDI or the network video feed really comes down to preference and your particular setup. Both SDI and the network feed are capable of providing a 1080p60 signal.
For example, someone may prefer SDI if the they are integrating the cameras into a system that is already utilizing a SDI switcher.
As far as choosing the 12X, 20X, or 30X models that would depend on the setup as well. There are cases where a 12X would be able to pick up the entire width of a stage when zoomed out but a 20X or 30X would not because the have a narrower FOV. There is a FOV calculator towards the bottom of the SDI product page.
thanks so much - that's really helpful.