With an external drive hooked up via USB2.0, can you tell the difference btwn 5900rpm and 7200rpm? Thanks.

#1 Before we answer your questions, we want to ask you: do you know what is USB 2.0 and what is rpm stand for?

There's no such thing as a free agent.

with 1.5tb externals going for $100, this is not a deal

#4, prove your case with links to better deals.

No #1, you can't. If performance matters, skip USB2 and move up to eSATA, or even SATA with a cable and PSU connector+ extension dangling out the back of the case if you must.

Hopefully in a year or so this will all be academic, then we'll see some USB3 enclosures, though personally I highly prefer buying a separate empty enclosure and drive, that way if one fails you can pull the drive out and have use of whichever still works without voiding the warranty, plus warranties on internal drives tend to be at least as long, often longer than external kits.

#6 - This has a 5 year warranty. So, being a Seagate, you will RMA this for warranty replacement about 9 times before the warranty runs out.