See the
Storage Review Main for details on WD Raptor vs other ATA/SCSI drives.
I don't think it has any articles on RAID vs Single... But no matter what RAID WILL give you a performance boost on loading, or HD intensive tasks. Like when i load games like BF1942 + CNC Renegade, and multiplayer maps, it's sooo much faster. It depends if you think it warrants the cost.
If your mobo has RAID 0 in SATA already, and u have the money, go for it!!! It's the setup i'm using right now. But i've never used a single Raptor setup before so i can't compare.
And the latency thing... i think it doesn't add a noticable amount of latency, much faster than any 7200rpm drive i've owned. Depends on what ur using for, and only you can really decide that.
Good luck!