how am I using it "incorrectly"?
how is it not a disappointment if it won't work at 9600 bps when presumably it's limitation is 57600 bps
Its limitation is 38400. If it isn't working at 9600, you are doing something incorrectly. I think we can be quite sure that nobody is using it like you do with any success, and nobody else has bothered to look at your code, which is mostly junk as far as comms is concerned. You can start with this bit
SoftwareSerial Serial1 (RX1, TX1);
SoftwareSerial Serial3 (RX3, TX3);
And while you are at it, you might consider including the software serial library, any software serial library, as you won't get far without it. Now I don't have any software serial libraries, but the examples in yours will surely tell you how to do that. Further, if you can't work out whether you have a Uno or a Mega in your hand, swapping it all for a train set would be a good idea. So you as well get rid of all that that Uno<>Mega stuff, as it may just be adding to your problem, and a simple "hello world" test would be well in order.
Since you have a Mega, you would be well-advised to read reply#5 again, twice.