I commute so I have the same route every day. I don't obsess about stops at lights or higher wind days. The most important metric is looking at a graph of my average speed over time and seeing if it goes up as my endurance/strength improve.

If you have a ride you do frequently, measuring your average speed during that ride over time will give you a sense of rate of improvement. There are just too many factors that influence speed to have the speed of any single ride be meaningful.