Earliest example of 'fast' zombies I can think of is Lenzi's Nightmare City which came out in 1980 (so it predates RotLD by 5 years).

Have this set up to watch tonight. ::cool::

NIGHTMARE CITY 1980


So I watched this. Took a bit to figure out if they were indeed zombies because I wasn't sure if there were any undead. There were. And they were fast as a human could be, not the frantic fast, and ugly as all get out. Again the fast zombies filled me with anxiety.