FTDI USB Serial Driver Buffer Sizes for Optimizing XBee Radio Throughput

I am attempting to optimize Digi XBee Series 2 Radio throughput. I have 2 XBee radios connected to my Ubuntu machine through USB ports with 2 USB->Serial FTDI cables that show up as /dev/ttyUSB0 and /dev/ttyUSB1.

Digi's Website gives examples of how to optimize thoughput with FTDI devices in this document: http://ift.tt/1DPzJqQ

However, that document only talks about Windows.

I know how to change the latency to 1 ms in Linux like this:

echo 1 > /sys/bus/usb-serial/devices/ttyUSB0/latency_timer

How do I change the Send and Receive Buffer sizes in Ubuntu Linux?

Thanks!