I love mine, it's an awesome saw. If a guy just wants to cut firewood and his firewood is easy to get to, it's probably overkill and overpriced. However, if you gotta do any hiking, cutting on uneven ground, chunking down spars, etc. the 500 works beautifully for that. Just the combination of the power, weight, and AV make it a dream to run.
I run the 400 the most out of my rear-handles, but the 500 is my 2nd most commonly used rear handle. If it's smaller-medium sized trees and/or with lots of brushing/limbing, I grab the 400 w/a 28lwb. If I'm just falling trees w/ little to no brushing, I like running that 500 w/ a 32" lwb. Both saws are easy on the body.