Originally Posted by jenni-m

It matters more over longer distances.

1 mile at 55 will take about 1 minute (and 5.4 seconds)
1 mile at 75 will take 48 seconds

25 miles at 55 will require at least 27 minutes and 30 seconds
25 miles at 75 takes at least 20 minutes

75 miles at 55 miles an hour will require 82 minutes, 22 minutes longer than if you traveled at 75 mph.