Sometimes you run into something that just rocks you back and makes you think. One page in a recent presentation by Sun's Fred Kohut had that effect on me.
The gear shown is roughly comparable on CPU, I/O, and memory - but
not cost, size, or power use. Bear in mind that the orginal Sun 10K was
the machine that
beat the System 390 so badly that IBM stopped publically benchmarking the mainframe.
Here's Fred's page as a small jpg. Click on the image and you'll get the PDF (1.8MB) - good enough for you to do what Sun should do too: turn it into a poster.