MSU (Maximum transmission unit) and MSS (Maximum segment size) represent details of the communication protocol. MSU represents the maximum value that a layer can have and it's value is usually in bytes, and MSS represents the maximum segment size and it's usually in octets. None of these parameters represents the download speed.
If you want to use an Internet booster with a 3G modem, chances are that you won't feel any difference. Your Internet speed is determined by the hardware limitation of the modem and this can't be increased by a software solution.