Topic: Creating a 'Performance Dashboard' for a site.. any ideas?

I want to build a kind of 'performance dashboard' for this site i am working on.

The idea is this, The site i'm working on is a big old legacy project that is a project management tool at a advertising company for many users .. we want to get an idea of the sites performance, in terms of page load times, over the 100's of possible controllers + actions, in order to identify those which are slowest and most in need of optimisation.
Also generating a page with some nice statistical data to show the management would be a nice

So the idea is simply to save some data for the last X hundred / thousand page views for the site.
The data being similar to the output saved to the log files, eg:
Completed in 21ms (View: 7, DB: 2) |
as well as some proprietry info such as the user viewing the page. etc..

Im wondering if anyone has done something like this before. It feels like the kind of thing someone may have written a plug in or a Gem for or definitely something someone out there has probably done in detail before.

love to know what you all think