Good article and some excellent comments

Not much in here on RAID 50, which is rapidly becoming one of my favourite RAID levels for Data and Backups

Logs and Tempdb are definitely destined for RAID 10 (1+0, not 0+1 as has been pointed out), but RAID50 gets around a lot of the write penalty associated with RAID5 by spreading the writes out across multiple arrays.

As an example, if you have a 5 disk RAID5 array which can handle 100 IOPS, then striping this with an identical RAID5 array gives you 200 IOPS (in a perfect world, realistically probably only 190!).

One area which isn't discussed in here, and can have an enormous impact on RAID performance is stripe size. Ensuring that your stripe sizes are multiples of each other as you stack the RAID levels is crucial to maintaining performance. Ensuring that the OS disk cluster size is a multiple will also help things along nicely.