I have extension plates for the snowblower on my Unimog. When dealing with the really stiff drifts the plates add just enough resistance that I cannot push into a drift to break it up. In which case I have to remove them. But for normal (loose or lightly packed) snow the gathering plates work great. So I'd say if you have difficult conditions go with the wider blower. If you only deal with dry, loose snow the gathering plates work great. Wet snow is another issue -- but that's why they invented lubricating sprays.
That's a very good point. I hadn't thought about cutting into the banks with an extension and I usually end up doing that towards the end of the season, when the snow banks have frozen and thawed a few times. They're really hard then and I can imagine it would take a lot to force a wing into it. Most likely outcome is a bent wing or blower end plate, or the tractor gets pulled sideways or it just won't go.