I tried creating a new (Creative) world in 1.8, in singleplayer.
I expected it to load fine, just like in 1.7.10.

Instead, the game gets stuck on "Downloading terrain" for a while, then loads chunks very slowly.

It seems setting chunk distance higher than 16 before loading the world puts the internal server in ultra-slow mode.

Screenshot : http://i.imgur.com/FHYUniy.png