If you use Angelbird ssd's for library sample loading, then do not use it in a raid system. Angelbird works better when you use it for library loading as a normal hdd. It also recommended in this way by angelbird. I have 64 GB RAM and load everything via SSD. I am using Angelbird's SSD-PCIe Cards with Samsung and angelbird SSD's. Everything is loading fast enough and works stable. I recommend 64 GB RAM for using in big orchestral projects. I think about extend the RAM to 128 GB. At the moment 64 GB are more than enough, but I am sure in 1 year, after the 16 GB Ram-reels are available for lower prices, then I will extend the ram to the maximum in my mac pro. I have tested two 16 GB reels to reach 80 GB and it only worked in Mountain lion, but I sent them back because the reels were too expensive.
Dimension violins itself need 8GB RAM to work efficiently. By using MIR PRO you need more than 16GB RAM. I recommend 24 GB. If you use all instruments in one MAC PRO I recommend SSD's for system and libraries and 64GB RAM. It works fine.