Having flown for a regional and now kalitta I can say I'm never as tired as when I was flying 5-6 legs a day at my regional. Long days on the 74 really aren't like long days in the regional world. On a 16 hour flight I will likely sleep for about 4-5 hours of that. Also since we don't have pax and thus no door you can get up and stretch your legs and use the bathroom whenever you want when you are flying. It sounds kind of silly but not having to call flight attendants and go through that whole process really makes the flying more enjoyable. After doing this I wouldn't want to go back to the passenger world and a lot of people I talk to all say the same thing.
It's not as glamorous and you'll probably look like hot garbage when you're walking through the airport in Incheon on some of those days but it beats the hell out of spending a significant portion of the day walking through terminals to get to your plane, paying a fortune for crappy terminal food, and being a referee for the drama between flight attendants Cargo isn't for everyone and kalitta isn't for everyone but its perfect for me and I don't plan on leaving. Ymmv.