I’ve been using a 4Tb G-Speed es in a RAID5 configuration for a half hour show I’ve been editing for two years now. The show is 720p, AVCIntra format. I’ve had no issues at all. Plenty fast enough for general editing. I can get a season of the show (16 episodes) on the RAID. After that, I archive everything to removable drives, put them on the shelf and start a new season on the G Speed. I run an eSATA card in my MacPro.
E=MC2+/-2db