akaya-- The rate you're after is about 267 MB/s. This is well below the maximum rates we have achieved with our USB 3.0 products (which all transfer at the same rate).
You should be able to maintain this rate, but much will depend on your PC. You'll need to make sure the operating system will not interrupt your process for more time than is required to pull in the data that could be buffered. You will also want to make sure you use the on-board SDRAM as a large memory buffer to keep things moving.
One small correction, this is not 1/20 the speed of USB 3.0. USB 3.0 has a signaling rate of 5 Gbps, but this is well above the actual achievable rate due to overhead. For starters, the 8b10b encoding lops this off to an effective rate of 4 Gbps. (every 8 bits of data is converted to a 10 bit symbol that is sent over the physical interface). That leaves a theoretical maximum of 500 MB/s but that doesn't consider any protocol overhead, etc.