A lot of 4K content is now available on KODI and some standalones like Viva and Bee TV for movies and TV shows, no sport from what I can see on it.
I can definitely see the difference between 1080p and 4K from my projector on an 85 inch screen but I don't think it is as noticeable below 55 inch on a TV.
Sadly my download speed is usually only around 23 mbps so it is just a few mbps to slow, although for the last couple of weeks it has been around 28 mbps but even that is struggling to keep up with something streaming so I tend to download movies in 4K with HDR and Dolby Atmos if they are available, then watch them off my computer.
It's a toss up to me which is better, 4K or 3D as the extra definition and clarity of 4K over 1080p makes it appear almost like it is in 3D but then when I watch 3D I find it so immersive that I think it just about has the edge over 4K.
Now if they did 3D in 4K there would definitely be no contest but from what I can see you can only get 3D in 1080p and most of the stuff I get are in SBS or top and bottom so I guess that they are really only half 1080p for each eye.