Limited datarate for high speed data from sensor

Hello there,

I am using XEM7350-160T. I am trying to pipeout data from mock data generator to PC(USB3.0) through python.
The data has rate of 128MB/s (16bitx64MHz where frequency is generated via MMCM using 100MHz ui clock from MIG). I adopted the ramtest sample for this purposes.
I use wire as handshake when SDRAM has at least BLOCK_SIZE*1000 bytes in it. The data is piped out via BTpipe.
The issue I have is that the data rate to PC is only ~21MB/s. I used different BLOCK_SIZE (512, 1024, 16384), but the data rate is still the same.
Would you advise where I could take a look at to debug the issue? the bench given by pipetest sample shows that the maximum data rate is 310MB/s for my PC port
I timed both wire and BT pipe in python. The BT pipe takes pretty all of the time