Today I got up to 46 miles per hour and went 40 miles. The voltage at the start of the day read 152, and at the end of the day it read 144. So I'm sure I can go 50. Maybe more. We will see. I just don't have a need to go further yet, and I haven't tried just an all out speed test on flat land.
10 miles of today's trip was with about 100 pounds of gear, for my job. 10 other miles wit My wife and 40 pounds of cargo. Some big hills, and a ton of stop and go in the city between lights.
I'll try a max speed test soon, and I'm sure I'll hit 50 miles in a week or so. The batteries should be in top shape in a few weeks. I hear it takes 20-50 charge cycles to get them in tip top form.