Sorry, I have no real numbers for you.

We know already quite a few successful RME products that act as format converter, Octamic XTC to put an example, where latency is not an issue.

In this case the format conversion happens in the digital domain and this goes extremely fast, as you have no latency in terms of AD or DA conversion or transport over USB/... from/to the computer.

IMHO stand-alone mode doesn't matter, as audio data wouldn't cross USB anyway. Digital audio is being bridged between Dante and MADI.

But what might be important to note is, that it also depends a lot on your setup and what the final latency will be between the two end nodes of the communication depending on:
- the devices themselves on Dante/MADI side, you might need to add A/D and D/A converter latency
- at MADI side: how many devices are chained and create by this a serial bus where the forwarding of audio also has a little forwarding latency (at single speed 3 samples delay from device to device, at double speed 6/12 samples delay, see e.g. Octamic XTC manual chapter 10)
- at Dante side the network structure, whether audio only needs to be switched or routed

Side note: even AD/DA converter have nowadays a very low latency of only 5-6 samples even at single speed (~0,11-0,16ms), see manual of ADI-2 Pro FS R BE and Babyface Pro FS (chapter latency and monitoring).

So I am not quite sure whether the numbers alone from RME will give you much insight in terms of the end-to-end "performance" in terms of total latency.

It would perhaps be better to describe your complete use case, which devices are are connected and how and to detail your latency requirements / expectations in terms of the format conversion at the Digiface Dante in this particular setup.