Nasm Nasmus | 1.9/1.10 wither skeleton farm: 10 skulls per minute @nasmnasmus866 | Uploaded 8 years ago | Updated 5 minutes ago
Gnembon's video about subchunks and stuff:
youtube.com/watch?v=IF6Umbf28Y4

The conveyor belt video:
youtube.com/watch?v=6ZVNUU4puIU

Showing that redstone dust causes lag:
youtube.com/watch?v=pgpaGaNId6o

World download:
mega.nz/#!9ZIGDBAK!X98-xwYnpsBUzz2ZBkZaSr5U1h2VHDwMh9bULs-Qvi0

or

mediafire.com/?e8de7ybbzax4gle

The farm is at 700,-1100 in the nether.