Thinking about --connect-timeout=1 rather than --connect-timeout=600 and adding --lowest-speed-limit

[CicadaSeventeen]

If some of the mirrors are not available to connect due to, for example, network reason, then --connect-timeout=600 will prevent script to give up that mirror, so that lots of times can be wasted.

On the other hand, --connect-timeout=600 with -m0 will give up dead/unavailable mirrors at once.

Besides, --lowest-speed-limit can give up very slow mirrors, which can help to speed up downloading too.