X11 is snappy when both computers are on the local network, but as soon as the traffic has to travel over the internet X11 is unusably slow. VNC feels sluggish in that situation but it's still usable. xpra or nx can make X11 usable over the internet. I suspect something like xpra will be created for wayland.

In my experience, even on a local network X11 can be nearly unusably slow, especially over WIFI. The protocol has too many roundtrips.

Choppy network on WiFi? Read up on Bufferbloat:

https://gettys.wordpress.com/2010/12/03/introducing-the-crim...

http://www.bufferbloat.net/

hmm.. but what about Xzibit - a per window VNC app (https://github.com/tthurman/xzibit , http://www.youtube.com/watch?v=OLyjz2BuoEg )

I think it is basically sponsored by Collabora