I did quite a lot of testing before the summer and it's the same delay using DataPath SC SDI card as using the DataPath LC SDI card. I had the following setup:
Where I connected a SDI source (with frame numbers) to a splitter. One of the outputs of the splitter was connected to a computer equipped with a capture card. The signal was captured and transmitted using NDI to a WATCHMAX server that displayed the image on a low latency monitor. The other output from the splitter was connected directly to another identical monitor. The both screens were filmed with a 240 Hz camera so I could measure the frame offset.
For 720p60 and 720p59.94 I got 4 frames offset which is roughly 67 milliseconds. The type of content didn't really matter.
At this time I used NDI v2 and the current version 3 is probably slightly more efficient. I will try to find some time and test this with the updated SDK version and also 1080p60 and 2160p60 resolutions. We also got the BirdDog NDI converter today so we will test that one as well.
Just running the capture card locally in the WATCHMAX results in 2-2.5 frames latency between capture and display. So if 4 frames are acceptable then NDI is much more cost efficient since most of your servers doesn't need capture cards. Great when using WATCHPAX units.