Two Words: "TIRE WEIGHT"...........is the major difference. The Nitto - Terra Grappler in 285/60R18-120S is heavy, and the LT285/60R18-E-123S is heavy "er". NITTO, USA does not list the specific weight of their tires on their website and that is extremely unfortunate. You will have to send them an E-Mail and ask for specific tire weights.
On the other hand, VX KAT's choice of the new radical-looking COOPER - Zeon "LTZ" is just a baaaaaaaad-assssssssss tire and only weighs 49 lbs. Get the brand new COOPER - Zeon "LTZ" in P285/60R18 and never look back. Less Weight + Less Expensive = More Happy!!!