eSATA is even more of a reason that Thunderbolt is less of an issue on Mac Pro's. Backing up my 10TB Mac Pro went from a 2-day process on FW800 to about 12 hours with eSATA. But remember that Thunderbolt is a true 10Gbs each way interface - I've never gotten over 40MBs with FW800 or 120MBs with eSATA (1Gbs I think?), so Thunderbolt could lower my backup times to a few hours.
Most eSATA cards are 3Gb/s (~285MB/s) but there are few eSATA 6Gb/s cards too. If you were not using RAID, then 120MB/s was most likely the maximum of the HD.