About the performance increase stats. They arent wrong, but remember you're still going to an IDE drive which would slow down the speeds.
And for raid. There are different set ups for raid. RAID 1 and 5 are both taking multiple hard drives (2 hdds for RAID 1 and 3 hdds for RAID 5) and combine them into one larger virtual drive. So when you install a game it will store the data on both or all three drives. So if you have 2 80gb RAIDed hdds your system would say (check "My Computer") that it is 1 160gb hdd.
Raid 0 is storing the same data on two drives. This allows
A: your data to be securely backed up
B: faster access times (loads BF2 alot faster)
C: Saves money from having to buy a 10,000 RPM drive to get quick access times
Then there is RAID 0+1 (my favorite) it takes 2 HDDs and makes them into one virtual drive but you store your data across 2 sets (2 hdds in a set) of drives. This allows
A: backed up data
B: faster access times
C: all your data stored on one virtual drive
D: lots of uninterrupted space.
If you still didnt understand this see this
RAID Watercoolers
I recommend that you use the same HDD's (whether it be 2, 3 or 4). If you didnt this could confuse your system.