K-man there is no real time table. If the shocks are still working well then there is no need to change it. If you notice they are not operating smoothly of if you want to change the handling then you should change it out.

zviper I would say between 50 and 80 should give you a good spread. Any lower and its going to be too thin for the weight of the hellfire. Any heavier then 80 with the temps you get up there and it will probably slow the damping too much.