what is the difference between the 520GV and the 200 GV ?

The big difference is in the sole. The 200 GV uses a "Power Matic" sole which consists of a rubber bottom, Asolo/Vibram midsole in PU triple-density. The 520 GV uses a "Triple Power Structure" Asolo/Vibram rubber sole in PU (dual-density). The 200 GV is also slightly lighter. This is from the manufacturer about the 200 GV: "Highly technical and one-of-a-kind, the Asolo POWER MATIC sole is comprised of three different PU densities that are co-injected and molded together. The high-density front portion secures and guarantees maximum stability. The medium-density heel reduces shock and resulting fatigue during take-off and landing. Further shock absorption is obtained through the four strategically placed low-density cylinders that are linked from the outsole to the midsole. Gripped with a dual-density molded rubber outsole produced in conjunction with Vibram®, the arch area uses a very high-density rubber to maximize support over the long-haul while the balance of the outsole has self-cleaning lugs designed for optimum performance on varying types of terrain." This is from the manufacturer about the 520 GV: "The new TPS sole, designed by Asolo in partnership with Vibram®, incorporates three shock absorbers that correspond with the areas of foot that receive highest impact during activity. These shock absorbers can be identifi ed by their different color respect to the sole. The shock absorbers are created by combining two polyurethane layers - one of high and one of low density. These layers are individually coloured using a new and innovative technology. The TPS sole improves comfort, stability and has a very distinctive look."