I've never used the abacus, so I don't know if it speeds up your Steady Shot cast time. If it does, that's really schweet. If you don't use the 1:1 shot rotation macro, I can kinda see it messing up your timing, but if you do use one, it should be excellent.
Personally, I use the hourglass, and it's okay. I'm using a 3.10 speed crossbow because I don't have wolfslayer yet. I've seen BBW at least 4 times now, and he must not like my leet running skills, because he won't drop my gun! But even with my slow speed, it procs pretty often.