There are a few key differences between the KitchenAid 4.5 and 5 models. The first is size, as the 5 is slightly larger than the 4.5. This difference in size also means that the 5 can hold more food, so it's ideal for large families or entertaining guests. Additionally, the 5 has a higher wattage than the 4.5, meaning it will be able to power through tougher tasks like kneading bread dough or grinding meat. Finally, the 5 comes with an additional mixer attachment - a pasta roller - which isn't included with the 4.5. So if you're looking for a versatile stand mixer that can do it all, go for the KitchenAid 5; but if you're wanting a smaller machine or are on a budget, then go for the 4.5