keep one thing in mind. the brakes and frame on your moped were designed to go 30mph. they can probably tolerate the stress of going 40. and that's a long stretched out maybe. i don't think any mopeds were engineered to be safe (or even to hold together) at much higher speeds. at the very least, you will most likely exceed you brake's tolerance levels.
if you really want to go that fast, you should just get a motorcylce. part of the enjoyment of the moped is being able to ride a bit slower than most cars and relax. i love the fact that i can very easily stop to talk to people. every ride allows me to enjoy the scenery, not worry about whether or not my brakes will hold up.