Hi Carter,
I find that Rifles feel a little unresponsive compared with True Tempers. Its just a matter of personal preference with such things, you have to watch you dont take a set of shafts you arent 100% happy with, just because they give the best numbers on a launch monitor.
Generally, the lighter the shaft you can control the better. Lighter shafts mean increased clubhead speed and a higher launch angle and a bit more spin.
I would say one thing about
callaway irons though, they tend to be quite heavy in the head so a slighly stiffer but lighter shaft might be good for them since it would keep the weight of the club down, but the stiffer shaft would keep the heavy head from overpowering the whole club.
Good Luck
D.