IMO you are better off with a Buriza, even a non-upped one. It has a builtin 80%ias, level dependent maxdmg, max piercing and 32-196 cold dmg (very useful vs PIs). You need only 15% more ias to reach the 95% breakpoint (which you can reach easily without socketing it), but further speed improvements are pointless. In hell mode you will reach its limits, as its base speed is too slow - it's like suicide if you are strafe-locked for too long. Then it's time to switch to something quicker, like BotD crusader bow, WF, upped WW string, M'avina's etc.