I wouldn't fill a hard drive more than 70 percent; the performance comes to a crawl as it fills up. The spin rate will help during the initial transfer to some extent - if you are copying data from another hard drive. If you are loading new discs, the CD-ROM is the bottleneck, not the hard drive. I would get two green drives and run them as a striped RAID for faster transfer rates (which will help speed data transfer to your backup, which I recommend).
Another option is the Drobo device, which is like a RAID but tolerates drive failures with less user headache than a RAID.
If you are paranoid, buy Enterprise class drives with the 5 year warranty. The price difference may be worth the piece of mind, especially if you've invested time and hassle of ripping your own CDs. I ripped about 250 discs onto my HD and it was tedious and I have still to fix all the metadata. I don't want to duplicate my efforts and would rather lay out for the data redundancy.
Another option is the Drobo device, which is like a RAID but tolerates drive failures with less user headache than a RAID.
If you are paranoid, buy Enterprise class drives with the 5 year warranty. The price difference may be worth the piece of mind, especially if you've invested time and hassle of ripping your own CDs. I ripped about 250 discs onto my HD and it was tedious and I have still to fix all the metadata. I don't want to duplicate my efforts and would rather lay out for the data redundancy.