I agree with the sentiment of most of these replies. Yes, it is possible to go 50 or 60 on an unpowered road or mountain bike down steep grades, but this is not safe for most e-bike riders. These high speeds are especially unsafe in congested urban areas with lots of intersections and it is certainly not considerate in bike lanes. There will be people, mostly young, who won't be able to resist the urge to use the speed unwisely and it will reflect badly on all e-bikers. When I was younger, I would have probably done it myself. Class 3 is enough for me and I even keep that to 20 - 22 MPH or less when riding in urban areas and around lots of other cyclists.
I like that Juiced offers a lot of bike for a reasonable price, but thumbs down to their 'off road only' 40MPH offering. If you want to go fast, get an electric scooter or motorcycle.