Hello,
yes, eSata to SSD would be fastest.
Foobar replied to some speedtests I made in this thread, recently:
http://forum.krontech.ca/index.php?topic=442.msg2321#msg2321(My tests are somewhere above his answer)
and shed some light on the Chronos' internal limits.
Basically, since most RAW formats are saved as image sequence, the size depending on recording speed and how big the section you want to save is: the smaller the files are, the faster the camera writes those sequences e.g. to a fast SSD.
USB sticks or SD cards usually get into serious trouble if they have to write say a 100kbyte file times 20000, as fast as possible.

All the best
Martin