well may I just say... you are connecting to one of the best towers. However if you are in benoni you are probably 10 - 15KM away from the tower (which is right on the boundry). A benoni tower will be up by the launch so that might help you in your area.
Another thing I have noticed is that people in area's with iffy signals (Which would be you) just plop the modem down somewhere and thats that. Indoor signals are not always good anyways, never mind 15KM from the base station, so what you need to do is find your sweet spot. Make sure its connected in USB and open the iBurst Terminal. Now move it around generally till you have a place where you get 3 bar on the device and 50 - 60% in the terminal, try everywhere, high, low tweak the arial and once you find an area where you have that sort of singnal, connect to the internet.
Apon connection you should watch the signal jump.. and now in the area where you got you 50 - 60% signal while dissconnected, move the modem around by an inch at a time untill you get the best signal you can possibly get (maybe 5 bar on the device and 90%) and try have a file downloading (multithreaded download, not firefox or internet explorer) the whole time while doing this to max the connection so you can watch your line speed down. As soon as you find a peak, that is your sweet spot, NEVER MOVE THE MODEM EVEN A MILLIMETRE FROM THE SWEET SPOT. Although from where you stay i dont think you'll get over 700kbps, but you never know. Welcome to wireless.