I believe it only needs 10 more IAS to reach the last breakpoint. don't hold me to that though. I use my demon machine plain and it is plenty fast for PvM. Adding that last breakpoint is only a bonus, its what 1 more shot every 3 seconds? You can do better by placing a rare jewel in it or the same by placing an IAS jewel in it.
Are you planning on making a ranged enchantress with that xbow? if so let me suggest razortail to take the pierce to 99%.