You can get enclosures that support USB2, Firewire and/or eSATA. If I didn't just buy a new Silverstone MS04 HDD enclosure for less than half of the typical price, I'd look for one that supports USB and eSATA or all three (add Firewire too). Then you could use a high performance SATA drive for those rare occasions when you can use the eSATA interface. USB and/or Firewire enclosures limit the transfer rate to under 40MB/sec so a high perf drive is a waste - get one that is high shock rated and reliable instead.
.bh.