I'm wondering why you are using RAID 5? Are the articles below outdated? I'm interested to know what is recommended.
http://carymillsap.blogspot.com/2009/04/what-would-you-do-with-8-disks.html

http://www.baarf.com/

http://www.mail-archive.com/oracle-l@fatcity.com/msg77062.html

In some companies, like the one I work at, the server/network group has so much power that you have no choice on the disk configuration you are allowed to use on "their" SAN. For this reason we have been forced to run 100% RAID5 with Oracle applications for over 5 years. The SAN techonlogy has improved with its caching and such and so far we are able to get the performance that we need even though we are RAID 5. The debate about RAID 5 has changed over the years with improvments in SAN technology so some of the articles are somewhat outdated but I assume are still all true if you want to insure the best possible performance. Some just have no say in the matter and you have to live with what is offered. To add to the debate it is very tied to the amount of load each system/application has. It is not a valid statement to say that you can never use RAID 5 regardless of the load and requirements of your system so a blanket type view cannot always be cost justified since RAID 10 and such add a lot of cost to the disk configuration. I guess my point is that as with almost everything it depends on your needs, your performance expecations, and your budget.