output's cache and performance

[eluser]Bad Penguin[/eluser]
I am trying to use $this->output->cache(600) to reduce loading time of my pages.

Is there a way to check if the served page has been generated from the cache or its a full live php codeigniter page?
I'm getting always 2.200 seconds as loading time.
The same version of the page as static HTML takes 0.043 seconds.

I wonder what is taking so much time:
- apache+php itself
- $this->output->cache(600); placeced in wrong position (i have it in MY_Controller.php)
- something else

Any suggestions?