The strongest two trees have been cut now. I think they'll be able to deal with it. They were getting ready for a second flush (new buds after this years spring flush started swelling) so I figured these were strong enough. And if not, that would be a good lesson for me.
I know that letting vigorous growth run causes backbudding, and I know that not cutting shoots would most likely improve backbudding. But the wood on these two trees is getting old. Branches are 30+cm in length (with 8 seasons of growth per branch), and there's only all of last years needles + this years. I'm afraid that if I don't push them towards forced backbudding now, the wood will become too old and I'll have to revert to grafting if I ever want to fill the tree up.
Most shoots were cut back to an equally balanced size of 7-14 sets of needles. So I might have just removed 5 pairs or so from the tip. It's somewhere in between cutting shoots and letting them be.
It might set me back a year or even two, it might help me out. We'll see what happens, I have the time, I'm just afraid the branches have had their time so it was now or never..
I'm taking notes so that if something works, I have a reference in the future. And if it didn't work, I'll have that reference as well. These aren't going to be show-worthy trees in the coming 10 years or so, so I don't mind screwing up a few times.