Triple high speed serial <> ethernet, which module should I use?

We’d like to build a triple serial (RS 422)<>ethernet converter with serial port speeds 3x500 kbps (real throughput would be about 3x381 kbps uplink, 3x10 kbps downlink).

Can you help me to choose an appropriate RCM module for this speed? Another issue is that we’ll need industrial operating temperatures (at least -40 to +85 deg C)…

Thanks a lot,
Ivo Strasil, EGMedical ltd.