Note the real-world sustained transfer rates on externals ... eSATA definitely a HUGE preference over USB3.
Hmmm ... surely they can spring for a second internal? One of the other options that would be spendier but fast for having all your material on "one" drive is a RAID of SSD drives, but needs to be large ones. Even just a second internal HDD and an external eSATA would be a big uptick over a single drive.