In my highly unscientific test I switched from a Dell 2650, perc ??, 7 mirror sets, NT and Oracle 8i to Sun v240, xraid (2 x 7 drive raid 5), Solaris and Oracle 9i. The performance of the 2 setups was very different. For the most part small datasets were faster, large datasets that hit the drives were much faster. Some queries were significantly slower, but could be fixed by rewriting them. The Solaris setup was much better under load and resulted in a measurable increase in uptime.
The workload is mostly read with some large batch reads. No large batch writes. The database does have a large amount of clob data.
In most cases I would say for the same money you are better off with more memory and raid 5 than less memory and raid 10. The problem is in the current world unless you run 64bit you can't get very much memory in a machine and drives are so large it does not take very many.
For cheap and fast I'd run dual AMD 64 with 2 SATA drives mirrored. You could get up to 16gig of memory and 250gig of disk for maybe 5K but no Oracle 64 bit support yet.
