Currently, the fastest transfer rates are with eSATA. As a Macintosh owner, I can use FW 800, 400, USB 2.0 and eSATA with a card. My rates with eSATA top out (with 1Tb drives) at 90Mb/sec. with ONE drive. FW 800 is about 60 to 70 Mb/sec. with one drive. USB 2.0 is a f-ing waste of time with external hard disks at a top transfer of about 25Mb/sec. I have just recently moved nearly ALL of my USB 2.0 drives out of their cases to two larger 4-bay eSATA cases for my Macintosh Pro! SansDigital have $140 enclosures with a PCI-e card that helped with this! (newegg and mwave)
BTW: I cannot begin to express the hatred I have with using large hard drives with USB 2.0. The manufacturers must have been smoking cr*ck. : ) They should have included eSATA and USB 2.0 with those drives..
As you can see, eSATA smokes nearly all of them even at eSATA 150 (150Mb/sec). The fastest version is 300Mb/sec for eSATA..
Right now the only way to locally saturate 10Gb would be with a sizable RAID at RAID 0, 5 or 6.
For example, if you were to take 10 2Tb hard disks (RAID 0) at 100Mb/sec you could yield (100Mb/disk * 10 drives) = 10 Gigabytes/sec.. which would more than saturate 10Gb Ethernet. These are very ROUGH numbers but they give an impression..