I'm an electrician, there is no OVERDRIVE. the watts of the bulb pull eletric through the ballast. the ballast never pushes electric out.
A larger bulb trying to pull a 1000 watts from a 600 watt ballast and you got overheating. What is going to give first ?
A 1000 watt ballast running at 600 watts runs kinda cool. Think about it.