You have 2 fundamental choices here:
Code First:
Design your models, and "wire" them up to your procedures that you have defined manually.
http://weblogs.asp.net/scottgu/archive/2010/07/16/code-first-development-with-entity-framework-4.aspx
http://entityframework.codeplex.com/wikipage?title=Code%20First%20Insert%2fUpdate%2fDelete%20Stored%20Procedure%20Mapping
Database First:
Point the EF at your DB and models will be created for you using your schema. You can always call your custom procedures using Helper classes etc.. You would pass in the EF model and extract the attributes needed.
Personally, I prefer to code first simple POCO objects and wire them up as I see fit. This gives you the most flexibility however it can get out of hand if you don't lay down an architecture first and abide by some governing patterns.
As for performance for high volume systems, similar to Ruby-On-Rails boiler plate MVC approaches can get unwieldy as they grow. Using efficient procedures for CRUD will always win out over dynamic SQL.