Timbgy, I have flown both, I have taken the 582 on a demo - but I own a 503 (so I am a little bit biased). I decided that it wasn't worth me upgrading because of my particular situation - custom built covered trailer suiting the square framed 503. The Hummer has heaps of power, and you get great lift from the larger prop that comes standard. I opted for a new trimmed chute (slower, but greater lift) and the longer, rubber edged, Bolly prop (more thrust = greater lift) - and I am as happy as a pig in p00!
Peter