Technically I'm not sure they are actually 380 sized inside but 'smaller than true 540' for sure. They are classed as 540's because what is measured is the external dimensions but in this case much of that is actually taken up by fins. The rotor size is a lot smaller than typical for a 540.

True.
There are alot of us running mildly boosted 10.5's in 4wd (and achieving faster lap times than when running 6.5's)