I get about 35 reps on 60% of max, so that weight may be good to do sets of 20 on. I would have short rests on such a weight (1m), but you will adjust accordingly to your own recovery needs.
I would normally do 4 sets of 10 on 60% with about 1 minute rest. That would be a solid session for me, but not gut busting. For others, that may be too light. Every 2 weeks though, I do a flat out set on leg press, either at about 10-20 reps which is about (60-70% of my max).
I always work out my training weights for all exercises based on my most recent flat out set. I get about 4 reps on 90%, 10 reps on 80%, and 20 reps on 70%. I test for may max on reps 6-20 depending on how i feel or exercise I use.
To make it easier to work out rather than try my mumbo jumbo, do an occasional flat out set for 20 reps, and then train on weight about 10-15% less for sets. You can adjust accordingly in terms of your own preferred intensity and/or recovery.
My Life Fitness leg press machine weighs 47kg, so I add that to weights to calculate.