[chef] different kind of clients, cookbook dev workflow

Hi there,

I've successfully setup a chef server and more than 100 clients.
I have two different kinds of clients: servers and workstations.

I read some of you would setup separate chef-server for this usage.

What's opscode's position about that kind of setup, and what would you
recommend ?
I can think of some reasons to use several environments:
- might be faster, would that mean chef-server doesn't scale properly ?

- attributes, cookbooks and node separation. As far as i know, there's
  no acl support in chef so I should not mix server and workstation up
  if I intend to have sensible informations in attributes, databags
  or cookbooks

- webui status page doesn't allow to sort, regroup or select nodes by
  roles


Another question for which the answer might be related:
What's your developpement workflow with cookbooks ?
Do you run another chef-server environment to test cookbooks ?
Using shef ?

I'm using git to manage my cookbooks, i'd love to have 2 main
branches "production" and "testing" and have chef serving the correct
branch depending on a node's environment attribute (for ex) :)

-- 
Laurent