I just read trough the thread and one thing kept bugging me the whole way. This is a thing that I think only Jeff Schewe has taken into account (that I noticed).
There was a lot of talk about 7200 and 10000rpm drives and then the better option, which is SSD - drives, debate about Trim and different Raid - levels.
But no-one except Jeff mentioned a raid controller. I don't know Macs too well, but since they are Intel based these days, I'm pretty sure they are basically the same when it comes to on board sata controllers (which suck big time).
If you really want performance out of your raid arrays, the only way to fly is an "third party" controller card. Preferably from a good manufacturer (Areca comes to mind) and which support Raid 6.
Why Raid 6 when my mobo does Raid 5?
Raid 5 is quite prone to hard-drive failures. Lets say that you buy 4 disks for your array. You'll probably go with same size disks (right), then you'll want same kind of drives for your array (right or wrong, depending), but the last thing will be the thing that'll probably bite you in the backside of things in the future. You buy them from the same place at the same time (definitely wrong).
This is fine when everything is fine. But these days when hard drives are cheap, you'll probably go with 1-2Tb drives. The problem starts to build up.
The next part is when they start failing (not if). They are bought at the same time, so they are probably from the same batch. They have been used about the same amount of time, so when one of them fails and you replace it, the controller starts to build the array again. During this time the activity is quite high on the disks and with large arrays the rebuild time is so long, that you are lucky if another drive doesn't go out during the rebuild. This is where Raid 5 fails, in the middle of the rebuild, another drive fails and the whole array is gone.
Raid 6 patches this a bit, since two drives can go, so it's reducing the possibility of a total failure, but then again, Raid 6 support is quite minimal (you'll have to go with the controller card), you'll have to get more disks for this to work and finally, Raid 6 is slower than Raid 5.
On that note, fake raid systems (mobo/software raid) are not really good, since Raid 0 and Raid 1 are the only ones that work even close to what they are supposed to. Raid 0 does make the I/O faster, but not by too much. Raid 1 is slower than one disk by itself and Raid 5 performance is a bad joke.
I use fake raid (Raid 1 arrays only) on my backup server, because it doesn't have to be that fast. Only thing I want is some redundancy. I do have two SSD - drives on my main rig in Raid 0, but that's because I wanted them to be a bit faster and also I wanted the combined space of 2 x 64Gb for my operating system.
What comes to Trim support and the lack of it, my disks are quite early and cheap versions, which are without Trim and I cant "feel" any slowing down yet (been using this installation of Win 7 for about 5 months).
And if you don't store anything important to the disks (Photoshop scratch, operating system (which is non critical to me) etc.) you can do a re-format with a linux live disk, so that your disks are returned to the state when they were brand new. That should fix the lack of Trim if you do it often enough.
These were just my 0.02$, so feel free to comment.