You're not providing any data to say having KeepAlive on would've 'crushed' the server, actually quite the opposite. For example - with KeepAlive on, your site response time was 5.31s. With KeepAlive off, it was 6.87s. So with your own test it was slower to load.

With keepalive off, your server would spawn new connections for every request rather than re-using them. With mpm-worker and threads, that's not so bad. However I've seen a lot of people run pre-fork which uses processes instead of threads which can be a Bad Time(tm) with heavy spikes in traffic.

Anyway - found this here (not my site) - explains it fairly well: http://abdussamad.com/archives/169-Apache-optimization:-Keep...