I feel pretty confident we're right. I just did 8 runs on the country road near my house, battery 60-65% during the test, outdoor temp at 45 but car had been through it's normal morning warmup and I'd driven for 40 min, tires were up to temp, it was happy. Full "throttle" was giving me repeatable results, traction control was "off"/dynamic mode, climate control off. Not very accurate, but I'd start from a stop at painted line and read the speedo (which lags, and is rounding) when the next mailbox crossed my a-pillar, coast on down the road and come back for another run.
58 run1 (I may have lined up a little different on the first run)