New DAE- Best practices for RAID setup

I just installed another DAE (our second one) on a Celerra NX4 system.  It has 12 x 600GB 15k RPM SAS drives.  For best practices I'm trying to figure out how to carve out the storage. 

On the DAE below it, I have a 6 disk RAID-5 and a 5 disk RAID-5 along with a hot spare.  I was told not too long ago that a 6 disk RAID-5 performs slower than a 5 disk RAID-5.

So if I put 2 x 5 disk RAID 5's, I'm left with 2 extra disks.

What about the performance of RAID-6?  Would 2 x RAID-6's be ok, or maybe 1 RAID-6 and 1 RAID-5 and 1 hot spare?

Thoughts, opinions?