I've really been struggling with this and when the commute is shorter then 10 miles it didnt' matter much at all overall and barely that much on longer commutes. Getting stuck at a light would make more of a difference. My commute has doubled and my wife is grumbling about it and doing all the wifey - we need to get your a car and you can't ride anymore I miss you I worry etc etc...

I started collecting data and using online calcs to estimate mild electric assist effects trying to chip away
MPH Round Trip Rolling Time
14 3:00 Really slacking off
14.5 2:54
15 2:48 Normal Pace
15.5 2:43
16 2:38
16.5 2:33 Serious effort but not racing
17 2:28
17.5 2:24
18 2:20 Electric assist territory
18.5 2:16
19 2:13
19.5 2:09
20 2:06

Even over a 42 mile round trip bumping it up just a little doesn't make that much difference. I'm really eyeng that electric assist territory though since I could do 5 days a week fast and still race on a few days and just not use the assist.