Here's a simple answer . Port forwarding WILL NOT increase your download speeds but yes it will help in case of torrents. If you do not have ports forwarded then other peer who get ur ip from tracker cannot connect to ur client but your client can properly connect to them . So it will just take more time for your torrent client to pick up speed since it has to connect to other peers and no peer is connecting back to it . After your torrent client connects to many peers you should get proper download speed .However when you are seeding a file you might have very less upload speed .