RAID 0 on four drives means that you will lose everything if any one of the drives fails. Not a quarter of the files. EVERYTHING. That's because your entire directory is striped across the drives, and losing any one of them means losing a chunk of the file system. And using four drives means that you have a higher chance of a failure. It's not four times the risk, because some failure scenarios involve multiple drives failing, but any failure means total data loss.
RAID 0 is intended for maximum performance but it's a big risk. It makes sense to use a RAID 0 volume as a staging area for stuff that you have backed up elsewhere. If you don't have it backed up, it doesn't belong on a RAID 0 volume.
I think you'd be much better off using an SSD. Or put the 4 x 320GB drives in RAID 5 - much less risky, and you still get a performance boost over using a single drive. I suspect the SSD will still be faster than the RAID 5.