You get more speed and acceleration and won't notice traction loss. It is somewhat of a myth that a mountain bike has to have fat really tires.
Weight is one of the most important variables in tire selection.
Rotational mass really adds up with only a few grams difference. The Continental Explorer Pro would meet your needs. It is light and can be used as a rear tire although it is supposedly designed as a front tire. It may slip on dusty or sandy flat rock surfaces. This is probably due to the wide tread spacing.