Collection by compare-at-price discount rate

[treithamer]

Hi, 

I would like to show products on Collections by discount rate only if compare-at-price has different price products.

So, creating a Collection I only see IF compare-at-price has a X price, but not percentaje

Let's say

SALE COLLECTIONS:

> 50 % OFF PRODUCTS

> 20 % OFF PRODUCT

Has anyone a recommendation on apps available for it? coding example? 

Thank you.