Yes it is worth it, generally don't gem for int. Choose either haste or mastery as your target. The int gems only happen at very high gear levels and the math is so fuzzy at that point anyway (makes no observable difference).
Aim for 12684. Haste increases DPS from bombs linearly, the breakpoints are just for proc triggering events. So the extra haste above the LB breakpoint isn't wasted at all, don't worry. You'll notice the duration of the DoT fluctuates with haste as well, that's a compensation mechanism which scales between breakpoints