A couple ideas. First, you can ask the hardware vendors for white papers, statistics, or references with actual installs (definitely do this since you'll get more than just performance info).
Also, do the same with Oracle (via your Oracle acct rep).
For Windows, you could try asking Microsoft. If they have any good numbers, they will probably share them with you; if not, then they probably aren't as good.
Another idea - pose the question to Oracle User Groups.
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The trouble with doing something right the first time is that nobody appreciates how difficult it was - Steven Wright