High-speed data read from onboard DAQ memory (non-NI product)

I have a non-NI DAQ that does acquisition at 250 MSPS and stores data on the DAQ board memory (4 GB). The DLL releases data stored from the memory in 1 MB blocks FIFO. However, I am unable to retrieve the data at acquisition rate even though I have high-end desktop, SSD, 64 GB RAM etc.

I noticed about 5 s delay to read 250 MS in LABVIEW 64 bit. The DAQ driver is in 64 bit. 

I heard from another person that the same DAQ even at lower system configuration can display data at much faster rate than the LABVIEW. They are using C++ and a regular desktop.

Any pointers?

Thanks