ダウンロード時のwgetまたはカールのダウンロード速度を制限します。

はい、wgetとカールの両方がダウンロード速度制限をサポートしています。どちらのオプションもマニュアルページに直接言及されています。

カール

   --limit-rate <speed>
          Specify the maximum transfer rate you want curl to use. 
           This feature is useful  if you  have a limited pipe and 
           you'd like your transfer not to use your entire bandwidth.

          The given speed is measured in bytes/second, unless a suffix 
          is appended.  Appending  'k'  or 'K' will count the number
          as kilobytes, 'm' or M' makes it megabytes, while 'g' or 'G' 
          makes it gigabytes. Examples: 200K, 3m and 1G.

たとえば、curl --limit-rate 423K

得る

   --limit-rate=amount
       Limit the download speed to amount bytes per second.  Amount may
       be expressed in bytes, kilobytes with the k suffix, or 
       megabytes with the m suffix.  For example, --limit-rate=20k will limit 
       the retrieval rate to 20KB/s.  This is useful when, for
       whatever reason, you don't want Wget to consume 
       the entire available bandwidth.

たとえば、wget --limit-rate=423k