Bill, you're right, what is heavy?
I think i should go as heavy as i can without compromising form.
The 150kg BS single on sunday for example, my legs could have lifted a lot more. But i didn't, because i felt my lower back. No pain, i just felt it more than my legs. And i changed my back squat from pushing the floor away to driving the sacrum up two weeks ago, so i left it with 150.
I think listening to your body is paramount here. A set of five can be more dangerous than a single, it's a question of form and control.