Two pretty different animals. The 570 is a trusted trail machine as long as it is not modified too much. Good quality and trusted by many. The 800 is vastly more powerful..closer to the 900, has the ability to handle mods better and haul higher loads. The 570 is a 50" and probably rides much like the 800 Trail but the EX will ride way better. Dependability...well, may be up to some luck, owner's attention to service, limitations and common sense.
Guess it boils-down to what the needs are and what the expectations will be for it's future.