Here are the key differences between the Siemens iQ700 washer-dryer models WN54C2070 and WN54C2A40:

## Capacity
- The WN54C2070 has a washing capacity of 9 kg and a drying capacity of 6 kg.
- The WN54C2A40 has a slightly larger washing capacity of 10.5 kg and the same drying capacity of 6 kg.

## Energy Efficiency
- The WN54C2070 has an energy efficiency class of A for washing and E for washing and drying combined.
- The WN54C2A40 has an energy efficiency class of D for the combined wash and dry cycle, though the washing cycle alone is also rated A.

## Features
- Both models feature Home Connect for remote monitoring and control, as well as similar advanced features like varioSpeed, speedPerfect, and autoDry. However, the WN54C2A40 may have additional or slightly different programme options and settings due to its different configuration.

## Dimensions and Design
- The WN54C2070 has dimensions of 848 mm x 598 mm x 590 mm, while the WN54C2A40 is slightly larger at 848 mm x 598 mm x 622 mm.

## Price and Additional Features
- The WN54C2A40 is priced higher, which may be due to the slightly larger washing capacity and any additional features or enhancements not present in the WN54C2070.

These differences highlight the variations in capacity, energy efficiency, and possibly some features, which could justify the price difference between the two models.