What is the difference between Audi A6 55 TFSI and A6 40 TDI?

I am a bit confused about the different model designations and what they mean. Can someone explain the difference between these two Audi A6 models in terms of engine type, performance, and fuel efficiency?

The Audi A6 55 TFSI has a more powerful and efficient gasoline engine compared to the A6 40 TDI which has a diesel engine. The A6 55 TFSI is also equipped with a 48-volt mild hybrid system for better fuel economy.

In terms of performance, the A6 55 TFSI accelerates faster and has a higher top speed compared to the A6 40 TDI. However, the A6 40 TDI is more fuel efficient and has a longer driving range on a full tank.