I have been riding motorcycles since 1999, not a stranger to going fast on 2-wheel among traffic.
6-7 years ago, I converted my downhill MTB into a high-speed street sled.
83v battery, capable of 40+mph on flat pavement with me onboard, (175 lb.)
I figure a downhill bike would handle the stress of extra speed on pavement better than regular MTB converted.
If you're not used to riding among traffic at higher speed than you can pedal on your own, you can easily get into trouble well beyond imagined with a high-speed capable e-bike.
300 lb. going at 40 mph; you will need some serious brakes to slow you down.
Start off with something sturdy, slower.. if you still need more speed after few hundred miles ridden, then look for other options.