Can one see a substantial difference between the video quality between a PTZ 30x NDI/HX and a SDI PTZ camera? And does one perform better under lower light situations?
The SDI and NDI models have the same hardware, so video quality and low light performance would be the same.
The only difference between the two models is that the NDI models come with an NDI license applied to them.
The NDI and SDI video feeds themselves should both be capable of providing a 1080p60 video feed.
The main advantage of NDI is that it allows for lower latency vs the traditional RTSP network feed that the SDI models use.
The latency with NDI should be comparable to the camera's SDI output but over the network.