I think the main difference is not the efficiency and the overload protection. The HX1200i is digitally controlled and therefore has more stable and accurate voltages. This is probably also the reason for the higher efficiency. It can also be monitored via USB with Corsair Link.
The power supply unit has 8 PCIe connections of type 6+2-pin, which can also be used as 12 V 2×6-pin connections. This provides a 12 V 2×6 pin connection for 600 W.
Was able to install it without any problems. I bought my own cables, so I didn't pay attention to the ones that came with it, but I thought they were sleeved.