While I'm new to the rails scene, and can't speak for the 2.x -> 3.0 performance change, what surprises me is that this post is upgrading because of newer gem support.

It this purely a rails upgrade? Or is the OP upgrading other gems at the same time?

You're using newrelic. Use it, and figure out exactly where it's getting slower. Do an entire stack trace. You can figure out exactly where those pages have gotten longer responses. Then you can suggest to the rails community what's slow for your application.

The platform is only as good as the community makes it to be. Maybe it's missing your case's optimizations because you haven't given specific feedback?