It is already known today.
As cosmic radiation increases exponentially above FL290 it is advisable to stay on Turboprops which are usually capped to FL250.
A lot less cabin altitude changes for your body to adapt to as well.
I never felt better as in my years on the Dash8, think of the higher jet pay as severance / risk premium pay. Why some Cabin Crew put up with all that radiation long term for a pittance is beyond me frankly.