sub-management of users

Hello,

I'd like to build a structure with "sub-management" of users.

I explain :
Somes users are simple anonymous users and can see content
Somes users are "RoleX" and have some specificities
Somes users are "RoleY"

And finally, I search a solution to enable "groups" of users from "RoleY" with an administrator, who can control, add, edit and delete users from it's own "group".

I have seen about the organic groups modules, tried to configure it for a solution but don't know how to enabled an "only per group" displaying list of users...

In other case, how to have some administrator users with access to user management, but can only manage users of it's own group ?

Is a good solution to use OG modules ? or another modules can be more efficient to do that ?

If anyone can help me it would be wonderful. Any url or suggestions will be apprecied

Thanks in advance

Thierry