What is the difference between MetroMax plastic shelving types?

MetroMax i is the strongest most versatile, corrosion proof system in the world. It is 100% polymer with Stainless Steel corner reinforcements. MetroMax i has a 15-year corrosion warranty. Holds 1000lbs per shelf & 2000lbs per unit. Usually, MetroMax i is the most expensive. 

MetroMax 4 has unrivaled value for an all-polymer shelving system. It is 100% all polymer, highly stable corrosion proof system, with a lifetime corrosion warranty. Holds 800lbs per shelf & 2000lbs per unit. 

MetroMax Q is a hybrid shelving system with rust proof polymer mats over rust resistant epoxy coated wire support structure. Each shelf also features a quick adjustment shelf realease to allow easy shelf adjustment after assembled. MetroMax Q has a 15-year corrosion warranty. Holds 800lbs per shelf & 2000lbs per unit.