Multiple U320 drives in a zero striped set down 2 channels. A good example would be 2 drives on one channel and the other 2 on another, or more. Use AppleRaid (disk utility) to build a 0 striped set.

With a single drive you aren't going to see much difference, at least you have the foundation to add more drives as you get them, they all must be the same capacity or they will get truncated to the lowest capacity drive.

A single drive won't do much more than a single SATA drive.

Christian