Have you considered going for multiple RAID 5 partitions and essentially "striping" your database across them?

For example you could have 4x RAID5 partitions (6 disks each). That way you only lose 1 disk per partition so you still have a partition size of 5x146GB = 730GB each.

You then create three extra data files for your database and rebuild Clustered Indexes so they spread out across the partitions evenly. If you have any HEAPs you can add and then remove a Clustered Index in order to spread them out across the disks. There is also a special way to do this for BLOB data if you have any tables that contain this.

It may not be as great as RAID 10 but the IO improvement would be a sure sight better than 1x RAID 5 partition and may even be better than 1x RAID10. I have done this for many large databases with significant performance gains. Unfortunately SQLIO will not be able to provide you with a good benchmark of this scenario as its a straightforward IO tool. If you could set up the "four-filer" database and test\replay your Application against it before going LIVE that would be the best bet.

hope this helps

P.S the assumption here is that your Log File (s) will be on a separate partition. If I am adding an external storage array to a server then I usually carve this up for data and use my internal disks as RAID1 or RAID10 for Logs.