Kills, Deaths, Creep kills, and other statistics don't matter when IP/XP is calculated.
The only real thing that matters is whether you win or not. You get some small bonuses if you win quickly or lose slowly. You also get a hefty bonus for your first win every 24 hours.
Slight variance in IP/XP gains, I'm guessing, depends on the ELO of the teams. I'm not sure if you get more for beating a team better than yours or if you get more for having a higher ELO in general, but it's not something you really have control over either way.