01 Sep 2008 at 23:35 - 25
I guess you can look at it this way also.
Due to the nature of crit scythe builds, there should always be some kind of crit boosting skills on your bar(way of the master, critical eye). Because of the 20% armor penetration, sundering increases with effectiveness the higher your base damage is on your weapons. This is why Sundering is great on scythes, but not so great on daggers. On a critical hit, the bonus damage you get from armor penetration is also factored in. Add Aura of Holy Might, and Asuran Scan, suddenly you have a significant boost in damage. Also, with a 20/20 scythe, 20% is about 1 every 5 hits, which isn't that rare. The sweet spot is how often you will get that sunder proc to overlap your successful critical hits.
Vamp on the other hand is the same damage on every attack, regardless of your weapon's base damage. The damage from vamp is the same if you hit normally, or if you get a critical hit. Usually the faster your attacks(IAS, double strike) with vamp, the more vamp will trigger, and the more damage you will do. Even in your example, vamp hitting 3 targets will trigger.
If you have a dervish, you can test the difference in damage between a non-crit, and crit attack with sundering. Take a dervish/warrior, with Wild Blow (auto crit), Asuran Scan, and Aura of Holy might. Use a Sundering Scythe and you can compare your top end damage, dps, or whatever strikes your fancy. .