It goes without saying to stay away from the cheapie eGay ones. The filament is not in exactly the right place, so affects the light distribution from the reflector etc. Also those blue ones are crap - they filter some of the infra red out and that makes them burn much hotter (the energy has to go somewhere).
I have used many high wattage H4 bulbs successfully in my various cars and bikes. The highest I used was a 130/90W but that was pushing it.
There are a few keys here:
The bulb itself makes heat. A 60W bulb is a 59,5W heater, and a 0,5W light. A 100W bulb is a 99W heater and a 1W light. This is just for info for now.
Loose connections (ie the spades inside the multi-pin connector) will be a resistance and a source of heat. I have taken to using ceramic connectors (available on eBay)

Pull the actual spades out of the connector and squeeze them gently with a pair of pliers to make sure they are tight on the spades.
Make sure any connections (wire) you make are good - preferably crimped with a heavy ferrule, or at least soldered.
Make sure that you aim it properly. Only thing worse then an poorly aimed light is a poorly aimed 100 watter! Because I'm often 2-up, I have the light aimed a bit low, but it's good when 'loaded'.
After fitting, monitor it the next couple of night-rides you do. As you switch off stick your hand in there and feel the wires and the back of the rubber boot over the bulb holder. They should be no more than warm.
Just one other thing: I don't use the 'pass' function. If you do, do so judiciously, as when you hit 'pass' both filaments are on, so you have roughly 4 time the heat generation going on. I guess it's only for a second it's okay, but be aware.
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