400 for an abused edge is reasonable and Adam nailed it. There is no one answer to this question. Like what's the best ice cream flavor. For some knives a mid grit 2-3 k or an aoto is a fine stopping point. For other knives the party is just beginning at 10k if I want to go to a 624k edge.
An orthopedic surgeon was once asked what too much force was and he suggested that you push it until it breaks .... and then back off a little next time
Not a very good surgeon btw.
Go to a higher grit and see if you like it ... and back off if it's too refined for your tastes.
Now that I see what I wrote, I'm really not adding anything new to the topic, so I'll just leave it as a +1 to what's already been said.