You don't need to send the whole world, just the area around the players location. Generally, an RTS game has both players starting together so there's no need to send any data initially. If you have a hot joinable game, then sending only the players immediate surroundings will help improve bandwidth. You should generally be sending delta's after the clients are synchronised. Perhaps expand on your requirements if that doesn't help?
But, as Apoch says, 50k should transfer pretty quickly.