Whoa...RAID discussions!
I do love talking about RAID.
It simply isn't as simple as a RAID0 will "smoke" a RAID1. While it is true that given the same circumstances or setup a RAID0 can outperform RAID1 it is mostly due to bandwidth as you say. But, of course, the more drives you have in the RAID0 will affect your write time. RPM is more of a determing factor in hard drive performance with 10,000 RPM drives in a RAID1 blowing away a RAID0 with 7200 RPM. Of course, that same RAID0 with Velociraptor WD drives would outperform the RAID1. A good RAID controller will satisfy two reads, one from each disk from a mirror. RAID0 is generally not used for critical data, databases, etc. but for very large files such as seen with video.
One never has to take a RAID5 offline if a disk goes bad. This is one of the advantages of RAID5. You simply plug in another drive and it rebuilds. If you have a hot spare, this is automatic. If you have a hot swappable, then you are in luck as you just throw it in. The formula for RAID5 is always N disks - 1 for space.
Adding a drive to a RAID5 does not make a RAID6. A RAID6 requires a controller than can support RAID6. RAID6 can lose two drives before it loses data and can afford to lose a drive while the array is being rebuilt without any data loss. RAID6 does not use two drives for parity. The first error-correcting drive is parity. The second form of error correction uses a Reed-Solomon code to implement Galois field algebra. This is why it requires a controller with more sophisticated computational capability. RAID6 disk space will always be N - 2 drives.
It generally is true that a RAID0 > 5 > 6 > 1 for READS, but it is not that simple for writes. RAID1 will often outperform RAIDs 5 and 6 depending on block sizes and write implementation.
RAID performance, implementation and what configuration to use will always be debated.
