i just bought a 2003 aprilia mx50 last week. it has already been fully derestricted and has an arrow racing end can. the speedo stops at 50mph but iv had mine well off the clock. my mate followed me in his car and i was hitting 65mph. the rev counter tops out at 12000rpm but it must rev to atleast 14000rpm. you dont need to do alot to the engine to make it any faster and anyway 65-70mph on a 50cc is amazing. u dont really need to go any faster. i very rarely take it to top speed. the engine just wouldnt cope with it at flat out all the time. to answer your question, all you need to do is fully derestrict it, racing exhaust(arrow giving you the best performance) and you half way there. iv just ordered a 14tooth front sprocket for my bike. my mate did the same to his rx50 and he got an extra 5mph. he fairly noticed the difference(in a much better way)