Its generally best to max the MB first and then a raid 0 if your still running out of ram. The raid 0 looks like 8-ssd's spanned across two Areca controllers with 4gb cache each. Should be quite speedy especially if the data is in cache. The random and sustained i/o for r/w will be impressive. I can always add more ssd's if need be??? The cost is dropping and the performance gets much better every six months.
Formatting the outer regions of the drive will help for sure and is cost effective as well compared to ssd. If you use some v-raptors even better.
Having your board full of ram is all very fine, which means you have a very large playground/working area, however, not having fast hard-drives to off load your work to, makes the large amount of ram almost worthless. Your system is only as good as your weakest link, to me, the weakest link in our current computer systems is the hard-drives, even though SSD's have come a long way, they are still the slowest in our systems.
Its like building the fastest airplane and not building a landing strip to land on or just not long enough :-) I am sure you get my point. Or Nascar with training tires on!
If you are working on 8x10" scan's at very high res 6400/8000dpi and work on it in photoshop, with several layers, you will end up with one very large file. Now if you want to keep those layers you will need to save it, and that will take time with one or two hard drives in your system only. Make it two SSD's in RAID-0 and it will help.
So with that in mind I think there are two things to bear in mind when working in Photoshop and similar applications, one is you need a large amount of ram to play in, where you can juggle your files around, but you also need fast Disk storages, to off-load these as quick as possible, a) to keep it saved while working b) to be able to quickly move to the next file.
Maybe your experience is different, if so I would love to hear about.
Just my $.02 again :-)