Dave:
Never seen that behavior before. They seem almost equal on my systems. Mongrel might be a slight bit slower, but it’s much more performant.
Are you running in development mode or production mode?
Yeah, I wouldn’t. But don’t rely on the logs too much for timings… grab a mac or a linux box and use httperf to test your sites. It’s more accurate. 
I spend a lot of time developing and deploying on Windows, so if you run into any other problems, let me know; I like to help.