I don't know that 5 SATA drives would be enough, it depends on how you plan to capture the HD-SDI path.
As far as whether or not this will work using SATA.... it will. If you look on HDFORINDIES, Mike recently captured uncompressed 4:4:4 to a SATA array from a telecine, did hours of footage, and NO dropped frames. He had an 8-drive SATA array. Raptors are not required for this kind of thing. But I really think you are going to need at least 8 drives if you are looking at doing uncompressed capture.
The PCI-x cards will give you enough speed.

Also, in your above prices, you listed Raptors as the SCSI solution. Raptors are SATA drives, NOT SCSI.

Jason