This entire thread is completely pointless because all the number theory means crap in actual practice.
Vamp will likely get you more DPS in ideal circumstances. It will also be blocked and negated to a point that the offensive total can be less than the degen penalty on you. It's situational and also dependent on playstyle to an extent. If you're getting a large number of hits in, it can be effective through some forms of prot.
Sundering gives you random bursts of damage. A random burst of damage can kill people. If you spike someone and they get protted/healed at a fragment of their health, there is a chance that if you had gotten a sundering hit in the spike they would have gone down. Damage at a point gets you kills in some situations, DPS gets it in others.
It is hard to select the better mod because of the situational and playstyle nature. There are amazing players that use either. Trying to say one mod is better because of a higher potential DPS in ideal circumstances is flawed as in actual combat circumstances vary, there are spikes, and so on. If you took all of that into account, which none of you have done or most likely will do, maybe you could get a solid answer.
You should probably read
this as well.