A Star Max may be a very good disc for you to try. It is at least as stable as a firebird, but much faster. You will get more distance.
However, you mentioned that you are trying to improve your game, which does not necessarily translate to more distance. If you want to improve your ability to throw any shot, then you would benefit greatly from learning to throw more understable discs on any line. This will force you to develope touch, and will improve your general accuracy tremendously. Also, if improving your game equals scoring better, then becoming a more consistant putter is probably the most important thing. This one guy has won 12 world championships, and I would guess that is because he putts better than anyone else, and is probably more accurate, too. His signature shot is a hyzer-flip up with a worn-in stable driver.