Question about Toshiba hard drive performance in Superdrive slot

Recently I modified my MacBook Pro (2011 model) by removing the superdrive, moving the original Toshiba 750 GB 5400 RPM drive to the superdrive spot and adding a Samsung 830 SSD to the spot where the Toshiba drive was located. Today I ran the Disk Speed app from Blackmagic Design and while the SSD performance numbers for sequential reads and writes were close to what's advertised for that model, the same performance test run on the Toshiba is showing about 55 MB/s sequential reads/writes. According to this site:

http://www.barefeats.com/mbps02.html I should be seeing about 105 MB/s performance. Can anyone verify that there is something amiss with my setup?