> but I think the speed is limited by how fast you can actually spin the cube faces.
I imagine the limits here are how fast you can turn your steppers against the friction combined with how fast you can turn the faces before he internal surfaces melt. It's possible that this cube doesn't melt simply because the operation only lasts a fraction of a second. Perhaps if this turn rate were sustained it'd fuse the internal surfaces. THAT experiment I want to see!
Yes, even though competition cubes are very fast and very easy to turn there is still friction. As an aside some pro cubers prefer to have a bit of a "scratchy" feel for tactile feedback... Humans are different to robots like that, we don't have perfect control.