What about a stability indicator that shows the amount of change in download speed?
For instance, when downloading a torrent, the speed slowly increases for the first few minutes and this affects the estimated time remaining a lot.
If there were to be an indicator next to the download speed indicator that shows the rate of change in download speed (derivative) as a percentage (+ or -), it would be much easier to see how 'stable' the current download is instead of only being able to see the estimated time remaining jumping from days/weeks to hours and then to minutes.