Okay, like I said, they are not photogenic....
Yet !! Couple of more years. Been topped once before, maybe twice on the power lined side. Both trees look better in-person than the pics indicated though. Basically, I thinned some interior bulk, shifted them away from the house and away from the lawn some to get light in. Cleared them from the power line to the house, and raised slightly to let the streetlight's light shine under one side.
This is one of them...
So, my guess was right. The cork / bark does produce friction. But the surprise was that the wood is softer like sweetgum (Liquidambar). So all-in-all, it was like cutting maple for effort: not too bad. In fact, it was a lot more fun to work on than I expected. The edges to the leaf are not very spiny, but I was concerned at the bulk at first, because the branch density was very comparable to old English holly, except that the cork oaks twigs are more flexible, and clean-up wasn't bad at all. Another suprise was how much visual improvement occured with every few cuts.
This was unlike any tree I've pruned, but was similar to characteristics of several types of trees I've pruned, all rolled into one tree.
The image below shows another first for me in business. (It's the other tree) I shaved away a lot of bark around these old cuts, so it would be easier in the next few years to see where callus tissue is coming from. I've never worked on a tree with bark thick enough at this age to hide the callus. The trunk below is a lot bigger than the image shows - the view shows it's narrow side. Not sure why the big-ass cuts were made, but the tree should do superbly as long as no more bad cutting occurs.
The fitst tree at the top, had two big limbs on the back toward the power lines that had sunburn damage on top, for about 4 linear feet on each limb. But only about a 2" wide strip right now and callusing nicely.