mod_gzip, zlib.output_compression or whatever way you compress your web pages is a great way of reducing your network traffic costs but comes at the cost of increased CPU usage. Despite what you might think, it can be more expensive to send data over the network, especially to slow clients than compress it first of all and send a smaller burst.
Unfortunately this little server may not be up to the task of gzipping content at an acceptable rate to make it worthwhile. I’ll leave it run for another few hours and check the stats tomorrow.