The maximum damage for the holy sword is 71-100; you might want to re-load a few more times, or try again at a higher character level. You may have done this, but if you quick save after the sacrifice, but before hitting alt or identifying the sword, you can quick load repeatedly to try to get the best sword.
Speed reduces the recuperation time, but you can not get below zero, so a high level of Sword Expertise makes this irrelevant.
If you have at least level 1 in Repair, durability is not critical, though a low value would necessitate more frequent repairs.
Stun is good; magical damage is good if you can get it, but I never looked for that specifically. A high Charm Quality could be good, and I wouldn't turn down a nice stat/health/mana bonus.
