http://www.reddit.com/r/Tribes/Here is the XP amount needed for each rank. The current maximum rank is 50.
Rank 6 is 17,000XP, takes 8 hours of playtime
Rank 19 is 250,000XP, takes 135 hours or 5 and a half days.
Rank 20 is 285,000XP
Rank 23 is 400,000XP, takes 190 hours or 8 days
Rank 24 is 470,000XP
Rank 40 is roughly 3,500,000XP, takes 1666 hours or 69 and a half days.
VIP status means you acquire 30% more XP every game (you acquire lifetime VIP status instantly when you buy any item or booster in-game)