Derbi is a must, de-restricing them invalidates licence as well as insurance, but the police in the uk dont know the differance between resricted or not. Tuning derbi's is easier, to derestrict remove carbrettor and take out the ring at the front nearest the engine, if there isnt 1 (as models change country to country) take off the exhaust and look for an oversized washer in the manifold.If it isnt here then ur in trouble,coz its expensive to do the rest.
1.Gearing, up it as high as yoou can 15 tooth front 41 or lower rear.
2.Electronic ignition, get some1 else to do this and ask for a rev booster to be fitted, if they say there is no such thing tell em to check out mine.
3.Fit race exhaust, jolly moto are the dogs bollox, and get the carb jetting kit otherwise the is no point, air filter if poss.
4.$$$$$ Extreme tuning, includes: Blue printing (ideal for the bike to rev out faster)
Crank lightening:very good idea, makes it rev harder.
Big bore kit: Get a Polini 1 if poss and get it seen too for port polishing and gas flow.
Otherthings like stage 2 or 3 even i have yet to look into, but my Festina Race Rep has all the above and does a genuine 75mph, only 8mph of the fastest gpr in the world.
The cost of this is unbelievable, I paid 1,800 pounds for mine, and at least a further 1000 to get going fast. I reckon another 500 will c it fit.