How many duplucate 5* heroes do you keep?

With HA10 churning mostly S1 heroes (with the occasional RNG blessing). I was wondering how many 5* dupes should you keep? Taking into account that only about once in 20 will give you a nonS1 hero.

Personally I still dont have Elkanen and Azlar from S1. So should I keep 2 + maybe 3 more?