How many times did you run the 256 one?

Before reading your post, 3 times; now 6. Always same results:

substr: >6.80
dot_eq: 10.2 .. 10.7
dot:    13.3 .. 13.6
[download]

This is perl, v5.8.8 built for i486-linux-gnu-thread-multi on Debian/Linux.