Just now saw this - I have been unable to get a batch redraw of DC's to not take significant time. It seems the more DC's you redraw in the same operation, the longer each successive one takes to redraw.
Eventually, I found a way around this by simply scrapping my usage of DC's and switching to groups. Operations on groups are essentially instantaneous.
I'd use DC's if it's one or few objects at a time, or something I want the user to be able to interact with via the DC interface, but most of my plugin's objects are not that - I'm manipulating them with my code. Since I'm doing Engineered Wood Products layouts on very large multifamily buildings, I end up with thousands of objects to manipulate, and DC's simply didn't work well enough, as they were too slow. And the fact that even changing one property - even one that doesn't affect geometry - forces you to have to redraw them each, that time involved was a deal-breaker.
