Building Enterprise level application using Codeigniter

[eluser]Nikhil Vijayan[/eluser]
I am planning to use Codeigniter for an enterprise level web application. which will have 2-3 million visitors per month .. the goal is to serve maximum users with minimal server resources..

So do u guys have any suggestions ,advice for me ?

Do u think its better NOT to use any frameworks ?

What about Active record , etc .. Does disabling Active record improve performance ? if yes why ? we are using mysql as DB so i dont need other db drivers so does disabling them help improve performance ? ...

Let me know what your experience using codeigniter is..

Between i will be also using matchbox for modular separation.

Looking forward to hear from u all...