How difficult is it to be consistent when “leaving another rep in the tank” on your all out sets?
On bench and press it is much harder for me, but this is probably because I'm only on cycle 2 and my understanding of the effect of accessories is very undeveloped. On both of these my power curve seems to be changing, so when I think I have two I suddenly hit a dramatic slowdown near the top and it turns out I had one, and probably finished with none.
In case your wondering, this does not bother me in the least.
Are you really tempted to beat or at least meet your last rep max at that weight?
I expect to always beat it. Again, this is partly because I'm only on cycle 2, so this attitude could be appropriate for up to 6 more months.
Do you find the technique to be a good way to find out about reading your body; in other words, would some of the increases come from the realization “wait, I actually do have a few left in the tank, I know this feeling, and it’s not the end yet”
Yes. But it's almost always about speed. When they slow down, you're near the end.
I’m hesitant to do any lifting without predefining the reps. It’s a hang up of mine. I do better with rules.
Well there are still rules. here's one: if you misjudge and the bar stops moving, drop it immediately.
You can't switch from predefined to all-out and not expect to misjudge a few times. If you never misjudge you're selling yourself short because you're not pushing the limit.