If you are throwing your Z XL 350ft and your Avenger SS 400ft, and you have only been playing for a few months, then I would say your max distance can take a backseat for a while. 400ft is a distance that most players don't even get too, without great form or some very inconsistant technique (I have friends that can bomb it out to 450ft with a sidearm or really muscle torquing a fast driver, but they maybe do it 10% of the time, and the rest of the time they are god-knows-where after their drive).
You should probably instead look to different kinds of drivers for max d, or work on your shots from 400ft and in.
A more stable disc at about the same speed as the XL would probably be a good idea, to get some more accuracy or to be able to hit some lines a little easier. An eagle, Teebird, or maybe a Tracker would be good.
Maybe you should add a more stable driver that is as understable as the Avenger SS. A Wraith, Surge, or Surge SS might be a good step up, as would an Orc, Z/ESP Avenger, or a Crush.
If you are throwing 350ft with the XL, and 400ft with the Avenger SS, and are new to the sport, congrats! Things are coming to you a lot easier than they do for most of us. Keep working that short game, expand your shot repetoire, and you'll be on your way.