oven spring temperature steam crust fluffy bread crumb

Hello, I have been avidly reading the forum posts on this site for a few months now. I find it the most comprehensive source of decent info about bread baking around.

I have one unanswered question though. 

I want really fluffy bread. I know that steam encourages oven spring by preventing the crust from hardening too early. I also know that bakers use a very high temperature in their professional ovens and that this somehow maximises oven spring.

But surely, the higher the temperature, the quicker the crust will harden, preventing further rising?