Bloodthirst – Siphoning health is 40% more effective and 80% more against bleeding foes.
So the change is decreasing the base bonus percent and adding the extra bit of siphoning versus bleeding enemies. This would make Dagger/Dagger and quickening thirst more appealing for necros.
That’s all :P
Edit: ok actually i’ll add more :P
You could say
Boodthirst – Siphoning health is 40% more effective and even more against bleeding foes.
The “even more” bit could be basing the bonus percent off the number of bleed stacks the enemy has. So for an example percent, say like 5% per bleed stack and only up to a maximum of 50% percent (only counting 10 stacks of bleed)