Well, that's a tricky one...
The RIAD-0 will give the better performance - 2 sets of heads moving independently coupled with double the data transfer bandwidth will easily out-perform a single set of heads even if the drive is spinning 33% faster.
You also double the chances of losing all your data if you have a disk crash. Lose one disk and you lose the content of both disks. If you run RAID-0 then backups are essential.
Personally I would never ever recommend RAID-0 for anything other than scratch-space (storage for files that don't matter if they get lost), but if the speed is that important and you're happy with doing the backups (I'd have 2 RAID-0 setups and mirror them on a regular basis or something similar) and to take the risk of data loss then go for the RAID-0.