FYI, if you use Toodledo and want tasks in Calendar and PI is too slow on 4s - solution
I used Pocket Informant and Toodledo on my Mini Retina and Android phone. When my (yet another) Android phone died, I decided to go with 4s (cost / no contract, and form factor).
Unfortunately, PI takes a good 5-6 seconds to cold start. May not sound like much, but when you need to glance at your week schedule in a hurry, it is an eternity.
After much experimenting with different calendars, I finally found one that has Toodledo support and is quick, PlanBe. I timed it and it's only 1 sec slower to cold start than the iOS calendar. Just like PI, it shows Toodledo tasks on the due date. $5 and well worth it imho.