I bought a 6600 just over a year ago--and I absolutely love it! I don't know much about the 5200 (which is retired), but one of my favorite features of the 6600 is the automatic thread cutter (which is not listed in the 5200 features). Two major pluses for the 6600 are the integrated walking foot and the larger harp, which really helps in quilting. If, on the other hand, you will be making a lot of clothing, you should consider that the 5200 has a free-arm, but the 6600 does not. Good luck, and you will be pleased with either machine!