Well, as I said above, I have no trouble getting to 4ms – honestly I haven’t tried to get it any lower because I can’t even hear 4ms of latency. There’s certainly no hit on system resources by running at that value; resource meter almost never breaks 20%. That said, I can’t have a full project playing with all plugs active at that low a value, there would be plenty of popping and dropouts. But I only ever need it that low for tracking, and I can disable the bells and whistles for that, then put it back to a high value and re-enable the plugs for editing/mixing.
This is the only real interface I’ve used, so I have no direct basis for comparison with other types. I did have an entry level USB interface right at first, but abandoned it for the 1616m after just a few months.