Thx for all the input. Yes I need a extra RAID controller. Most boards just have 6 Intel Sata ports and some have 4 more extra. So I would need at least a RAID Sata card with 4 ports.
Chris: on x58 chipset boards you do not want to populate all 4 (or slots - this incurs a performance hit, populate either 3 or 6, leave the 4th (8th) slot empty.
Do you mind expending on that ? it is the first time I have heard of it and I read a lot on computer sites. The X58 has a triple channel RAM interface, so one needs to use at least 3 slots. (for example 3 x 1GB) However o achieve 24Gb of ram one has to fill all 6 slots with 4GB mem. So far I haven't heard any negative comments. The one reason some people have problems filling them is, because they are using standard dual channel Mem, which isn't really the best choice for a triple channel board. (Yes dual channel RAM can work, but does not have to)
Here are my thoughts about why using three larger SSDs instead of smaller ones.
First it is speed. To get the best out of writing and reading speed one needs to use at least 128GB per SSD. (As I posted above, below that you loose speed especially write) I really don't worry about a drive failure. I have all my presets and stuff stored away and could set up a new system from scratch in around 1-2hours.
For the scratch disk, I probably will go with HDs around 1000 for SSDs is just to much for scratch. I can always change that in the future if the price drops a bit. (Still thinking on it)
In regards of CPUs, well the one main thing that puts me off the Xeon rout is, that the current generation isn't really new and still is really expensive if one wants to get the same speed.
I'm pretty sure, that one can't buy a dual Xeon System with 2,26ghz and expect it to hold up against a 3.6ghz i7 system. It just won't. Even if you have twice the cores. Especially in Lightroom and PS :@
So to get a real advantage of a Xeon workstation, these CPUs have to be around 2,7 ghz and here it get's really expensive.