All three will have the same shifting performance and durability (maybe slightly less for the 400 without the nickel plating) but I believe the higher the price, the lighter the weight and the HG-50 and 6500 will have a more polished nickel finish. The 6500 uses an aluminum spider for the larger cogs making the whole cassette lighter. I don't know the exact weights of each but if a few grams are not important or having shiny cogs, just go with the HG-400.