Hi gang, I am trying to nail down the difference between these sets. My understanding is that the 513 is a 313 with a built-in tuner and the 613 is the 413 with a built-in tuner. Are there any other differences? I also have heard that the 413 and 613 are capable of a better picture than the 313/ 513. I have no way to test this for myself. Is anyone familiar with them? Thanks!