You should max out if you want to - I think it's fun! It's not really a waste of a workout session, I don't think. It is very challenging of course, perhaps not as fatiguing but still a training stimulus all things considered.
Your 1RM can be calculated somewhat accurately by your 5RM - it could be somewhere around 90% of your 1RM. I think there is little point attempting to calculate it using such information like how many sets you were able to do at 5 reps for this weight, as your rest time between sets and your personal anaerobic conditioning can affect that without making much of a difference in terms of total force generating ability.
A few weeks on the grand scale of getting stronger is not much time at all comrade
you got this!