There is a significant amount of health risks associated with circadian rhythm disruptions.
As Fedelta has mentioned, maybe if you committed yourself to getting senior in your particular seat at FDX and being able to cherry pick the trips that are easiest on your body instead of chasing money, you'd be okay in the long run.
The human body was not meant to alternate sleep times day to day for decades on end though -- just keep that in mind. It can only do "sleep when you're tired, eat when you're hungry" for so long before vital systems become effected. Besides actual sleep disorders, other things are regulated by your circadian rhythm and if you keep screwing with it, they get messed up too (blood pressure, metabolism, endocrine system, variable heart rate, body temperature, etc.) I am not a doctor so you might want to check out some sources because the topic is not one to be ignored.
In this same category, I have talked to SWA pilots that prefer the PM schedule that have said they had not set an alarm clock in weeks or months particularly if they live in base. Or, if you're an early bird, you can get that every workday and be done at noon-3PM.
So, this is one category of many that you have to compare side by side. But I certainly would put this one right up there with retirement, vacation, and so on, if I were in your position.