Haha, no... ...thread is not closed...
I asked you where it snapped because the place where it snapped IS the problem. It seems the nut has created some pressure on the string and as a result, weakened and cut it. (FYI, the nut is that piece of either bone/plastic/metal thing at the start of the fret board, also known as the zero fret where the string always rest on.)
It might have been friction or sharply-cut grooves in the nut which cause the part where your strings slide across it to break. This is a common problem with frequent adjustment of tuning and one way to solve this would be to clean and lubricate the grooves (the 6 slots on the nut, one for each string) when you change strings.
Here's how:
When no strings are on, use a sharp and strong object, eg toothpicks, together with tissue to clear the grit/rust/dust/dirt in the 6 slots.
Get a .5 pencil lead (2B to 6B is fine) and coat the slots with it. The graphite should make the slots smoother.
Load strings on as per normal and it should not break when changing tunings frequently again.
As for getting .11s i would advise you against it unless you are sure you'll not use normal tuning. If you change frequently from EADGBE to CGCFAD, a good compromise would be .10s. Though not the best gauge for that drop C, it make it fairly easy to bend on normal tuning.