In order to hit 35 (about 56 km/h for me), I had to drill out my airbox, use a biturbo, change my 31t rear sprocket to 28t, and upjet my main jet to 62, and idle jet to 32. A lot of time went into tuning my idle mixture for a good takeoff. I'm still trying to determine if my main jet is the correct size. Plug chops only give you part of the picture.
But every bike, setting, etc., is different. You really do have to learn as you go along. I think the best thing for you to do is to try one thing at a time. ie: add a biturbo, and upjet a size or two to see what the difference is. Then you can start trying other things as you learn more and do more reading. Reading and actually feeling your engine four-stroke at top speed (telling you that you need to downjet) are two entirely different things.
I can tell you that the hill-climbing performance with the stock gear and pipe are better than what a smaller rear sprocket and biturbo will give you. The Biturbo is tuned for more top end, at the expense of low-end power. Hill-climbing is first gear is whack, though. Any classic moped with only one gear will struggle way, way more than you do.