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.
I promise you my little server was getting more traffic than that, and since patio11 -- another vocal "turn off KeepAlive" advocate -- personally commented in that thread that turning off KeepAlive directly resolved their site outage, I think I'm going to stick with what I've got.
The server is already using mpm-worker, as well as fcgid carefully tuned to make PHP nice and snappy without eating all of the server's available memory.
Final point: site response times aren't the only metric a server admin should care about. A server admin should also -- and maybe even primarily -- care about concurrent connections. If I can serve thousands of simultaneous connections at 6.87s or hundreds of simultaneous connections at 5.31s, guess which one I choose?
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...