Okay, I have done some testing now with the quantum boots in combination with armor and jetpack and they show quite different behaviours depending on the situation.
Versions I used are: Forge 3.1.3.101; IC² 1.95b.
I tested drops of around 40-50 blocks while I was wearing ONLY the quantum boots. From that height I lost 2.5 hearts and it didn't matter if I was holding CTRL while falling. Also I tried I jump from the same height (which increased the falling distance by 10 I guess) and lost around 5 hearts then.
Now another test with quantum boots and the rest of armor to be nano armor, the jump then didn't make me lose any hearts (I still heard the fall damage sound though). I don't know if you can enchant nano armor, but this one wasn't.
Also I tested the jetpack together with quantum boots. When you fly high enough and drop down while you don't at any point fly up again during the way back down, you get the same heart damage as you would from just dropping down. However, if I fly upwards just a little bit before I hit the ground I land smoothly without even getting the sound of fall damage.
All of this looks like quite weird inconsistent behaviour of the quantum boots, especially the fact that the presence of a nano armor reduces the fall damage. Is it supposed to be like that? Are the boots supposed to maybe spread the fall damage to all the other armor pieces?!