Can't decide which boost to buy? BUY BOTH

Apparently if you get both Timed and Per-Win boosts, they stack multiplicatively, giving you waaaay more than 2x IP. It seems to fluctuate a tiny bit, but it's roughly 3x to almost 5x more IP, as you can see in this screenshot where I earned over 1000 IP from a single game (IP boosts aren't affected by your win-of-the-day or party reward bonus).

Suddenly, buying new champions and runes doesn't seem so hard anymore.