In theory, you could achieve the same level of muscle exhaustion by doing just 1 rep but at the same time you open yourself up to a tremendous opportunity for injury.
Yup, that's why I always go for lighter weights because I don't have the time to be injured.
and you are doing it the smart way! Do you write down your progress from one session to the next?
I don't. I should probably do that.
I usually just do it until I feel a bit sore.