The reason you don't want 55w on your low beam is not due to the heat buildup in the housing so much as the heat build up in your wiring your low beam is set to draw no more than 45w so pulling 55w through it may damage it (it being the wiring not the housing) due to heat buildup in the wiring more power means more heat.
why do people always say this? stock low beam bulb is 55 watts and high is 65 watts.