Both the 757 and 767 can safely land at any weight up to the maximum takeoff weight and that can differ considerably from the declared max landing weights (up to 28t for the 757 and 44t for the 767-300).
At any weight over the declared maximum landing weight, as has been pointed out, an overweight landing check must be completed and due consideration given to landing distance, approach speed vs landing flap speed limits (for the 767-300) and brake temperatures.