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 high end material.
Your latter-mentioned fabric (breathable rating: 5,000g, waterproof rating: 5,000mm) fits right in the mid-range. I would assume it is a mid-end material.
Does this mean that the higher end material is better for you? Not necessarily. There are many other factors that should be considered such as intended climate, quality of construction, care requirements, warranty, and price.
