Yes, I guess paying extra for MS500i is worth it for doing even 80 cords. Didn't even know that saw existed until your post,572 is heavy for the power.
Around 2.5lbs per horse power
MS500i is about same weight and almost 2hp more.
I've run 660, 500i, 460, 362, 361, 2100xp, 395, 372, and many others I can't remember.
Currently have a 500i and a 460.
Used to do 350-400 cords a year, but just do it as a hobby now. Did about 80 cords last year.

I think the Echo's have a good niche for home owners where they have pro-saw durability/reliability, but not quite the performance, but still miles ahead of a department store saw.