It's my view that most of these comments from real "experiences" compliment each other.
Chris' "variable castor" theory is simple geometry, it is bound to vary with normal undulations, and after a lift, that range simply shifts up a peg, or two depending on the lift.
My truck with 4" lift appeared to be fine on cc bushes, but after a lift, these trucks drive very differently, and you re-learn all the new driving characteristics.
In my case, I had a bent axle casing soon after the lift, so not knowing it had happened, I learned the new characteristics along with the effects of the bent casing.
After replacing the casing, it all changed again, noticeably for the better, but it still didn't feel "right" somehow, the biggest dislike of all being its sensitivity to be pulled to one side or the other when hitting standing water on one side.
The only thing going through my head was castor, but the geometry check at that time, showed everything in tolerance. Anyway, I went ahead with the change to drop boxes, and it was like a eureka moment, the truck drove like a new one, such a massive improvement, almost unbelievable.
It's just my experience, I'm sure Chris has a point that the plates are perfectly adequate for a 2" lift, I've never had one so I wouldn't know. But if you go for 4" or more, I would strongly recommend the boxes.