do I mount rack apps in Rails (3.1) for faster APIs?


I'm not sure I fully appreciate the best use(s) for Rack apps (e.g.,
Sinatra apps) in a Rails (3.1) application...

Scenario: I have in mind a bunch of RESTful controller actions linked
to models -- all for providing an API.

Approach 1: handle each resource from its own mounted Rack app:

+ 'Rails 3 in Action' advises mounted rack apps for Rails APIs because
they are *faster*
+ If I ever decide to split out the resources into their own
individual rack apps, I will have the rack server code and associated
tests already written

Approach 2: ignore the mounted app approach and separate out common
controller behavior into an ActionController mixin and associated
tests and configure for each resource

+ I've done this before, so I know it works, and won't take as much
time as Approach 1, which will be new to me

Any thoughts?