yeah, so basically, 10's are very versitile- you can play almost anything and sound good doing it. 9's you lose some of that sound and they are thinner so you get that breaking problem.

the higher the gauge, the richer it sounds, but also they're harder to play on. for big bends and stuff like you say you do, i would recomend the 10's. they arnt so thick that you cant easilly do huge bends on them, or tap, etc.

and theyre thick enough that they wont break as easilly, as well as they will have a fuller sound.

and about the tuning down... well im not gunna lie, ive never broken a string when tuning down. true, its probably torture on your strings if you keep tuning up down up down, repeat. if your gunna tune, you should probably leave it on that tuning for a long time.