Your comparing 2 different types of CPUs.
Since intel is not a 64 bit chip it cannot run the 64 bit Windows. If this is important to you, then look no further then AMD. Both Intel and AMD are changing how their chips will be very shortly, so whatever you buy now, it will not be upgradable in the near future. If you don’t need the PC right now i’d stay away from high end (3 GHZ+) systems.
IMO the cost is too high for the short time they will be upgradable.
As for the RAID question, SATA is different from IDE that it is hot swapable meaning you can physically remove a SATA drive while the computer remains on.
Erik