That is 5*T7 tanks at 2000. Not bad at all. I really like your list.
Rangers are useful for objectives in cover, denying space for enemy deep strikers and the occasional mortal wound. They also excel at picking out low wound enemey characters (painboy, warlock, IG psykers). The strategem that makes them 6 to hit can be useful (assuming you run them as alaitoc).
I like the falcon. Yes, the wave serpent is probably superior, and better value point for point. But I find that the pulse laser, combined with a bright lance makes it a different vehicle to the serpent. So in answer to your question, I'd start with upgrading the weapon on your falcons.
Is there a third troop choice you can fit in to your first list to fill out the batallion?
I like dire avengers and howling banshees in falcons. The banshees as they are fast enough to be an assault threat, even if the falcon is well behind the serpents. The avengers simply to score objectives.
I'm curious to know how your vypers with bright lances go. I am guessing that they can't be ignored by your opponent, who finds them harder than he expects to take them down when all his big guns are pointed at your hover tanks.