Agree 100%. I always use a 3x for anything sized 3,4,5, or 6 (3/32, 4/32, 5/32, 6/32 inch diameters). -6 is harder to do, but those are pretty rare for what I do (small aircraft).
A 1x or 2x gun just doesn't have enough impact force to set -4 or -5 rivets without first work hardening them. I...