First of all I am building this prototype, so I can investigate sending commands to a simulated robot, and streaming video from it using GStreamer. You can check out some issues with streaming, and about GStreamer here and here, respectively.
The Xbee 2mW Module is 250kbps Max data rate (1200m). The Xbee explorer dongle is easy way to connect it via USB. Pin assignments are in this datasheet http://www.farnell.com/datasheets/27606.pdf .. I'll stick the same things on the base station (which is just going to be my PC at present). For the modem, I'm just using HUAWEI E3531 in HiLink CDC-Ethernet Mode. I did a tutorial about using this with RPi here if anyone wants to use it as serial modem btw!
So, I'm not sure how this is going to go software-wise, because I would just have normally connected the RF and modem directly to the robot - rather than have them externally on another microprocessor! So I don't want to say much until I figure this out a bit!