Cruise ship internet service is provided by satellite, as far as I know everyone uses the same system. It's unlikely one line would be much better than another.
That said speed depends on usage, everyone on the ship shares one connection and it's dependent on how good the signal is. If the weather is bad it will interfere and be very bad if it works at all.
Best times to use are in good weather when everyone is asleep, let's say 2am-4am. With the time difference this could be ideal for you but don't count on it being dependable.
11 cruises in 2012, 90 nights at sea visiting 15 countries
8 cruises in 2013, 56 nights at sea visiting 7 countries
Next cruise: None scheduled
PM me if you need a cruisemate for any Europe, transatlantic, or Panama Canal cruises
Date, ship, cost pp