Oh hey, missed this thread.
Core+UA+Completes? Basically SRD & Complete right? Reason I ask on the SRD part is the SRD includes the Epic Level Handbook. The none-epic Enhance Item feat found in the ELH on page 114 adjusts the Save DCs to reflect the crafter's ability modifier rather than the minimum, so if this bow it pumping out Slaying Arrows it would in turn change those Save DCs.
The Save DC of a Slaying Arrow is 20 and broken down it is 10 for the base, +7 for Finger of Death's Spell Level, and +3 for the 17 minimum needed to cast it. Enhance Item & 34 Int/Wis/Cha would make this DC 29, a 9 point improvement. Of course, who said 34 was the highest possible score you could get?
So the first step is to get a
good version of this bow, then build around it.