Intel is offering the ability to test drive Oracle 10g on Windows 2003 and Red Hat Linux running on Itanium 2 processors. I can't think of a better way for you to find out about the performance for your application which will give you insight into the scalability of your application which can help you decide at least about acquisition costs. That's absolute concrete data to start.
HP has a TCO calculator for Oracle on HP with Linux as well that allows you to gain some insight into how a Risc/Unix (specifically Sun) might benefit from moving to the HP Proliant servers. It's obviously sponsored by a vendor but taking the source with a grain of salt I think it's a useful tool.
This was first published in January 2005