People who have performance drives *already* use eSATA (seriously, firewire? Is this 2002? Worse, you then go on to talk about CPU usage, where again the answer is "use eSATA")
eSATA is a nice technology in general, and certainly looks like the future of commodity high-speed external storage, but I expect that it will take a couple of years before the OS/driver support matures. As evidence: take a random sampling of eSATA host controllers and you'll find a disturbingly small percentage that provide driver hooks to safely unmount the drive. You'll find an even smaller percentage that does this *reliably*.
1394 drivers are pretty mature these days, so one doesn't tend to run into those sorts of issues. 1394b also gets close to 80MB/s in practice (not just in theory); it takes a pretty fast HDD to saturate that kind of bandwidth. I would argue that 1394 is still a pretty good choice in 2009, although it's clearly on the way out.