There is a difference between random read and sustained read. Random for HDDs can be below 1MB/s depending on how small the files are. Basically hard drives need to seek for files which adds time. Transfering 1 x 25GB file would be much much faster than transfering 2300 files at 10mb each. If you factor in fragmentation it seems about right.
Here is my RAID 0 array with Western Digital RAID Edition drives doing single large file and a million small files.