I'd like to know this as well. Some of my Coworkers went to RailsCon a few weeks ago and were remarking how a speaker talked about how they scaled from tens of thousands of hits a month to a couple hundred thousand hits a month. Not very encouraging when that's the sort of traffic we get in an hour and the solution was to use nearly double the amount of web and memcached servers than we do now on our PHP stack.
You can't compare servers to servers. Each app has its own computational needs and caching rules. Your hit is not my hit. One site might simply render a template, another might perform 20 queries and generate giant complex docs.
While it's true you can't do 1 to 1 the fact that my site does ~700 times as much traffic, and it is absolutely the latter of your two types time ten is a cause for caution. This is why I want to hear from some actual enterprise level people that have solved real scaling problems, unfortunately at the conf it seemed like startup size scaling problems were being addressed, and perhaps not very well.
