Apply the bigest discount

Apply the bigest discount

I have two related questions with the Special Promotion extension,
  1. Is it possible to configure two different rules and only apply the maximum discount of both of them?
  2. If there is a rule that apply a 20% discount for some categories and there is a product of the same category with a special price (15% off) it's possible to apply just the rule over the normal price (without the 15% off)