I have noticed a significant slowdown when editing tables with horizontal
lines compared with the same table without the horizontal line.  Currently
tested in 7.9.2 and the version in elpa (7.9.3e i think?).

Editing the table I have now, 12 columns, about 60 rows is nearly instant
when the table doesn't have any horizontal lines, but when it does contain
such lines, just inserting a character in a cell cause a delay of several
seconds.  Seems to be related to the number of rows too I guess, because it
only became noticeable when the table got over a given number of rows.

-- 
  Peder Stray