Zee, having cleaned the bitrot, works fast. (luarocks install zee-git-1.rockspec should work now.) I suspect this is a clue:
Author: Reuben Thomas <address@hidden
Date: Wed Oct 3 02:13:44 2012 +0100
search.lua: simplify find_substr to allow only searching from point
As a result, remove the last calls to tostring for the entire buffer
contents, and make searching the buffer much more efficient.
Also remove the non-regex search option, which is no longer used.
I can't find a corresponding commit in Zile.