CodeIgniter - resource intensive?

[eluser]mikemike[/eluser]
Hi guys,

Myself and a colleague have been rolling out CI sites for a while now and use it in most of our projects. We've done some small projects recently that have exploded in popularity. We end up getting around 400,000 visits per day across several small (in code size) sites.

Recently, however, we've had some server issues. We have quite a hefty server for these sites. We have plenty of spare RAM and HD space, but it appears we're lacking substantially in CPU power. The server spec is below:

Code:

Dedicated CPU
2.4GHz
RAM
1504MB
Storage
40GB
Bandwidth
1000GB

These sites are probably best off in some sort of bespoke system. The system is basically just a series of plain text pages with a maximum of 100 words on each. The only images on the site are those from the layout - of which there are about 5, largest being the logo at 25kb. The others are 2kb or less.

We chose CI for these small projects for scalability. We know we can easily plug in functionality and we know the framework inside out. We really don't want to have to re-write the systems in something bespoke and fast, but CI is becoming far too sluggish for us to use.

My question is, what can we do to help improve the speed of CI with CPU in mind? Are there any best practices? We're not currently using caching, does that make a huge difference?

It might be worth noting that it was our hosts who gave us the information on CI using lots of CPU, so if you feel that CI isn't resource intensive at all, then please let us know!

Thanks