mention in --limit-rate that --speed-limit might ruin the limiting slightly.

docs/curl.1

@@ -447,10 +447,13 @@ 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 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.
+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.
+
+If you are also using the \fI--speed-limit\fP option, that option will take
+precedence and might cripple the rate-limiting slightly, to help keeping the
+speed-limit logic working.
 
 This option was introduced in curl 7.10.