why no wattage is given has an easy answer, it will be higher when you put more load on a system. till it blows up basicly.
also temperature has great effect on a system's performance, when the battery is cold it doesn't work as good versus a bit warmer but motor and controller will be more efficient when colder.
in offroad even the dirt has significant effects on the systems, when you have lots of resistance in soft dirt your car will need more power to drive true it.
List goes on, i could be typing till tommorow night.