Slow Transfer Speed on Certain Files

Model : ReadyNAS 104

Configuration : Raid 0 (2x 1TB Drives)

Drives : Western Digital Blacks 1TB 7200RPM

HDD Tune Sector Scan and Smart Tests pass all green, read and write tests on drives show 146.9MB/sec | 15.9ms Access Time | 158.8 MB/sec Burst Rates

issue : Folder containing business critical information reads and writes at slow speeds (256KB/sec avg). After following other threads and discussions and trying balancing, scrubbing, defragging, firmware updates I managed to get the read and write speeds up a bit (2~3MB/sec), but this is still gonna be too slow for my users needs. 

What I tried : Moved all files onto my computers solid state drive and transfered to seperate internal hard disk drive, writes around 110MB/sec (I assume not an issue with the files themselves now) || Tried transfering a seperate file (5GB game file) to the NAS from my computer through the network which writes around 60MB/s (the NAS is capable of writing quickly) || Tried transfering the files to my Home NAS (I own one as well) which normally reads/writes between 20~35MB/sec however it gave same behavior as my customers NAS sending at about 2MB/sec || Tried connecting an external HDD 2.5" to the NAS directly via USB and transfer files through the NAS web browser utility however I can only assume the transfer rates are slow, it doesnt give me the data rates but the 30GB file size advised it would take 42 hours to finish

Folder Information : 30GB size | 350 folders | docx, xlsx, and pptx are the only file types in the folders

other thoughts : was hoping to get at least a 10MB/sec transfer rate, the issue is not isolated to slow data rates when transfering files but mainly with accessing them. My customer doesnt move files at all really, they just modify them. Opening windows explorer and going into the folder names is extremely slow and sometimes will time out. Once the files are open saving them will sometimes fail due to timeout error messages or file cannot be accessed message. I have a total of 4x 1TB drives but only 2x of them are used for data storage, the others were used as backup drives, the behavior is present on all drives, even external ones, also on my home NAS as well, any thoughts as to this would be most helpful.