Good question. Without getting too technical, both garments are “waterproof/breathable” and for casual usage would not appear to be too different; however under more intense conditions (internally via sweat or externally via snow/rain) you would most likely notice a difference. 
Waterproof/breathable fabrics resist droplets or water from passing (outside-in) while allowing water vapor through (inside-out). Typical mid-range fabrics tend to have values of 5,000g of breathability and 5,000mm of water resistance. From this we can determine that the first fabric you mention (breathable rating:20,000g, waterproof rating: 20,000mm) is a very aggressive claim of very high waterproofing and breathability combined and I would assume it is hig
Waterproof/breathable fabrics resist droplets or water from passing (outside-in) while allowing water vapor through (inside-out). Typical mid-range fabrics tend to have values of 5,000g of breathability and 5,000mm of water resistance. From this we can determine that the first fabric you mention (breathable rating:20,000g, waterproof rating: 20,000mm) is a very aggressive claim of very high waterproofing and breathability combined and I would assume it is hig