Those old smokey 2-stroke mopeds are chain driven and not good hill climbers. At least they are light enough, you can walk them up a hill. A 50 cc modern scooter..like the Aprilia Sportcity 4-stroke 50cc, has a speed of about 42mph and will climb very steep hills with the CVT. In other words, they out-perform legal e-bikes by a wide margin. They need to be registered as motorcycles though, which is one disadvantage. Hill climbing is the problem with legal e-bikes. By the time you have enough power to tackle hills with motor power alone, they won't be legal. I'm talking about real hills though, like you find in San Franisco and Hill Country, Texas where I live. Without being able to change gears on an e-bike motor, it would probably still be possible to make a great hill-climber and stay within 750 watts and 36 volts, but it would be pretty slow. On the other hand, the DD motors which are great for speed are lousy hill climbers. Maybe a geared motor on the back and a DD motor on the front would give you the best of both worlds. Pretty expensive though, but if you compare it to a small 50 cc scooter, maybe not any more expensive over time.