This value really IS in bytes/s (not for the total), and apparently 56
kB/s is too optimistic. The value was used by LL for transfers that went
beyond the total download time (2 minutes?), adding enough seconds per
received bytes to the timeout to allow a download at 56 kB/s to finish.
Our meaning is different however: we time out immediately and whenever
the download drops below this speed.
Perhaps a better algorithm is where the speed demand is based on the
total size of the download, but I'm not sure we always know the size of
downloads at this point.