There are actually a few factors when trying to decide what's faster when it comes to hard drives.
The variables are access time, burst read speed, average read speed, and sustained read speed.
The raptors excel in areas such as access speed and burst speed. This is especially helpful for loading a lot of smaller files in a quick manner (ie video games). This also improves the time it takes for programs to begn loading.
Slower RAIDed drives excell in average and sustained data read speeds. These speeds are usually considerably faster than a single non RAIDed raptor. The best use for slower rpm RAID arrays is for large file storage. They do however offer a bit faster burst speed than say if u were to take one of the drives and use it singularly.
It really depends on what you want the drive for mate. Gaming? Raptors are superior drives. A/V editing and the likes? Slower RAID drives FTW.
Hope that helps a bit!
Edit: Raptors can be some noisy buggers... like when ur defragging, they literally sound like a dieing llama. Standard read/write operation they aren too bad. Other drives out there are definitely more quiet though.