Allow a wider range of acceptable download times

# Limits on what download times are too fast/slow/etc.
download_toofast = 1
download_min = 5
download_target = 6
download_max = 10

We could use shorter download times, but we're trying to match torflow.

We could allow a wider range of acceptable times. In particular, 5 and 6 are very close together. Let's try at least a 4x range, and see if that helps?

download_min = 4
download_target = 8
download_max = 16