When changing guitar strings, it's worth taking a little extra time to give the nut slots and bridge grooves a quick rub with a soft lead pencil. This seems to make tuning easier, as well as reducing breakages on the more vulnerable 3rd and 4th strings.

When a string does give out, it usually happens when I'm thrashing the box in a futile attempt to compete with massed fiddles and squeeze-boxes. However, in more sober moments, it does seem to me that beyond a certain point, hitting the strings harder doesn't actually produce any more volume. so, if volume is your highest priority, you might consider taking up the fiddle, the accordian, or even the bagpipes.

Alternatively,if you want to get a little more volume out of a guitar without battering the strings quite so hard, I can recommend fitting a set of brass bridge pins.

Wassail!