What do you mean by intensity? Whether or not they're going to failure? I'd hope by now that's been established as irrelevant.
The weight was sufficient that they sustained damage that would necessitate repair and growth. It would have to be a weight they were unaccustomed to.
Also you gotta remember, there are two mechanisms of recovery: 1) repair of damage (this causes growth) 2) Neural recovery from a training bout. These occur independently of one another.
The general concept of "the more weight you lift the more recovery time is needed," is wrong. It's a leftover from Jones-Mentzer non-science. How much recovery time you need is related to how much volume you did and how much was taken to failure.
So back to your example, if our theoretical dude can deadlift 800 for a 1RM, 600 isn't gonna put a dent in him. Recovery time? A few minutes. If 600 is his 1RM? Probably days. It's more about the weight relative to your ability and how much effort you exerted in lifting it. Closer to failure = more recovery time needed.