You are complaining about images taking forever, spiking CPU and LOAD... probably JS and CSS as well.

This way you are effectively only serving the actual content and AJAX from your machine with which its designed to do vs straight file serving.

I think your VPS is IO Bound and memory bound and caching *WAY* to little with not enough memory for the bare metal and it shows with FileSystem IO.

I'm betting if you do an iostat (from the systat package in CentOS) and watch it a while... you might just see something.

I think a CDN will benefit you greatly.