So I'm a fan of Joel, and I saw that the stats on his Rescue stacks hasn't been inserted yet. So I did the stat research myself haha.
The conclusion of it is:
Heal Cap Up:
1 Stack (+45%)
2 Stack (+60%)
3 Stack (+75%)
4 Stack (+90%)
5 Stack (+100%)
Attack Modifier
1 Stack (+15%)
2 Stack (+20%)
3 Stack (+25%)
4 Stack (+30%)
5 Stack (+35%)
Multi Attack Rate (don't have enough data for the lower stacks)
5 Stack (DA 90%/TA 20%)