I wouldn't expect any at low draws - if there was you'd be hard-pressed to notice anything.. If you had a thermal camera that would be a quick way to visually see the losses. High loads for sure there would be some sort of losses
And if you dont want that heat we generally say max 1/2 of their raiting. XT contacts are known to work on RC and thus you only run for minutes at a time and then the heat that is generated is not a problem since it will cool down in short again.
The cable used will be very important, too.
A thicker cable will act as a heatsink and more efficiently draw away any heat generated in the connector. You can even use an oversized cable, and trim away a few strands at the tip until it fits in the connector. Use plenty of solder! Keep adding until nothing more goes in, to maximize electrical/thermal contact with the connector.