W/o exact measurements i would say that based on my own exp. it is easier to shed some weight -7-10lb (either from bike, faster /lighter tires /bodyweighy )is ideal and that would equalize the 400wh battery with the benefits of the 500wh bat. W/o inccuring the additional cost . In a few years a 900wh , 1kw battery would be common place.
Ex. In 2015 the brand i have (easy motion )!had a 416wh batteries , in 2019 some of their bikes have now a 750wh battery.
The highest level of assist, so it would be 28mph and then a little more with the bike unlocked with BikespeedRS. My motor is a Bosch Performance Speed.
16-17 miles on a 400wh battery is with a semi-upright posture on Haibike Trekking S commuter bike. My route is flat with 150ft of elevation gain. I’m estimating that my whole setup with me, the bike, and two panniers is a little over 200lbs.