For SATA vs SAS I think it comes down to whether or not SATA will be sufficient for your I/O needs. SATA can find a place in any business if you're needing lots of storage and don't mind the performance hit?
Have you been using multiple RAID 1 arrays in the servers? The advantage RAID 10 will bring is that your disk I/O will be spread out across all drives rather than trying to balance I/O across multiple RAID 1 arrays. You might also consider RAID 5 to maximize storage, but RAID will generally edge out RAID 5 for performance especially for write I/O.