The only "work" you need to do is to keep track of anything that may be a factor in your ET's & MPH.
You didn't say during what times of the day and the overall order of the runs you made. (i.e.: L, L, R, L, R.)
"Usually" early morning or later evening will provide best ET's with slower times in the middle of the day. Wind, weather fronts, humidity, temperature, jetting, water temps, shift points, etc., etc., etc. are all factors. You need to know why you were consistent that day and know how all the factors may affect that consistency in the future so you can predict and dial-in to compensate. Conditions may not be the same next time. If you are doing things consistently in the driver's seat, then it's that much less you have to be concerned about.
I have an Autometer playback tach which has been VERY helpful in keeping track of when I do things right or wrong and consistently or not.
MPH can be a good indicator of the affect a breeze/wind and its direction can have between runs.
.....nice numbers, if you can't work with that, you need to find another line of work.... 
