It is all about access time not spindle speed and besides 2 x 10000 rpm does not equal 20000 rpm total. Scsi still has fast seek times which is why playback can be better. The disk is able to randomly access the data faster. Remember that unlike a non linear editing system the Mac has no way of knowing what you want it to do next with Catalyst. So it is really depends on how fast the system can get to any piece of data with no notice.

A RAIDs real advantage is its ability to capture or play out a wide bandwidth of data in one hit. You need the balance of both with Catalyst or any media server. A single high speed SCSI drive tends to have that balance.

If you look back through the forum you will see a lot of posts about this including some speed tests that Richard did some time ago.

Personally I use an Xserve RAID which uses some really heavy handed caching in its onboard RAM to give really consistent playback of many layers. Prior to that I used Raptors set up in 4 drive raids.

Obviously it is all about what you can afford and what level of performance you need.

Have a bit of a read on the Barefeats.com and Macgurus.com websites where they explain both technologies fairly well.

Cheers

Toby