Sorry I don't
However, simply being NDI doesn't tell anyone sufficient info... really
NDI is NOT natively supported. so how are you getting NDI into OBS Studio?
I use Panasonic NDI PTZ cameras... and I use their Virtual USB driver (no NDI Tools, OBS Studio plugins, etc) . different approaches may have different performance impacts
And which version of NDI? and which settings? Which resolution and frame rate, etc. some NDI (ex HX) use more compression to use less bandwidth... at cost of CPU to decompress...
And then does your setup enable GPU decode, or are you CPU limited for incoming video processing?
And then, what kind of PC? I can think of workstation with 80+ cores and a TB of RAM and 10GbE NIC... that will handle a LOT more than a consumer PC .. so by definition the answer is bound to be 'it depends'. Using NDI instead of SDI will move some workload to NIC vs PCie (or USB, depending on how your SDI feeds into OBS Studio PC)... or are you using an external video switcher (which would be completely different. Presuming your current OBS Studio PC has all 8 SDI feeds, I would NOT assume NDI load would be all that different (but I'm only guessing... based on heavy impact would be processing 8 simultaneous video feeds, not the specific data path to CPU/RAM)
if you are using an external video switcher, and your current OBS Studio PC only sees a single video feed, then a change to NDI would be quite large
I have a single 1080p60 NDI PTZ camera now... with 2 more arriving any day now... a single camera uses around 28+MB/s bandwidth. on a i7-10700k, my OBS machine is barely busy... I suspect with 3 NDI cameras (whoohoo) load will go up... shall be interesting to see by how much. 4K would obviously be a much higher load... but I don't have such a camera to test with