4K or 5K Content for your riMac

Looking for some good ultra-def content to watch on your riMac? So am I. The various youtube videos I've run across that are supposedly offered in 4K, none of them are very good. They seem to run at 20 fps or worse.

Here's an impressive movie made with Blender and rendered in near 4K, and itplays like a cinema movie. It's a 6.7GB download, but worth it. What else are you going to do with your 3TB drive?

http://mango.blender.org/download/

I have no affiliation with the above. But I was pleasantly surprised to find this after searching videos online.

 

Thanks!

So here's a question. In order to watch 4K videos in all their glory, do you have to set your riMac screen resolution to native 5120x2880 before watching the video?

Or is Quicktime Player smart enough to render it at full 4K detail even though it is running under a 2560x1440 desktop resolution?