"what I'm asking - although there is an 11 oz total weight difference - in practical use there is only a 5.5 oz difference."
I'd say the impact is far more than having 11oz. I can't imagine it would be less.
When you are using trekking poles there is constant acceleration and deceleration going on, so you are doing a lot more than just suspending the mass (like you do with stuff in your backpack). When you push off of a pole, you then need to lift that pole up and accelerate it forward at a high rate of speed so that it passes you, decelerates and lands it front for your next step. So the mass of your poles is constantly being accelerated up/down and forward/backward by the muscles in your arms and wrists. This is particularly pronounced at the bottom of the poles. The handles of the poles move sort of at a constant speed, but the speed of the bottom of the pole is constantly fluctuating radically as the tips accelerate, move quickly and then stop.
Comparatively, weight on your back moves in a fairly constant vector. The speed remains pretty steady, and it does bounce up and down a little, but it's not moving around nearly as much as a trekking pole tip....so mostly you are just suspending the weight and not really accelerating/decelerating it too much.
To illustrate what I'm saying, imagine adding a 5 lbs weight each to the bottom your trekking poles vs. adding 5 lbs to your pack. It would totally suck. You could hardly walk. 5 lbs in your pack on the other hand would slow you a bit, but not nearly as much.
Now with the LT4 poles, you've got virtually no weight in the bottom half of the poles since they only weigh 4oz and half of that is probably in the handle. When you walk with these, they whip forward so effortlessly. If you switch back to other poles its noticeably more work. You may not notice the work if you've never used super light poles, but there is a real difference and it's more pronounced than 11oz would be on your back.