Image quality
Shortness of the 5x-42×56 brings in more Chromatic Aberration and to control that we use Super ED lenses (High Master lens system) in the 5x-42×56 Wide Angle Scope. But as the IQ is different between the center and the peripheral part due to the nature of the Wide Angle eyepiece, some people may find the image quality of 5x-42×56 less than 5x-40×56 GEN II. If edge-to-edge clarity is important to you, we recommend the 5x-40×56 GEN II. ( Internal optical structure of the 5x-40×56 GEN II is the same as the 5x-40×56).
Also, in any riflescope the best image quality is at or near the center of the adjustments.
5x-42×56 riflescope has an internal adjustment range of 40MIL; 20 up, 20 down.
Because of the very wide adjustment range of this riflescope, you may experience some image quality degradation as you near the limits of the adjustment range. This can occur because of the extreme refraction of the incoming light at the edges of the objective lens. This degradation will worsen as the magnification increases but if you readjust the focus turret each time, you will be able to see the image clearly. In case you do not wish to adjust each time, we recommend using an appropriate canted rail if you plan to use this riflescope consistently near the limits of the adjustment range and at higher magnification. It can be utilised to gain additional elevation and to keep the scope optically centred as much as possible.

Temperature anti drift lens system

5x-42×56 Wide Angle scope incorporates Temperature anti-drift lens system so that it will naturally adapt to changes in temperature and maintain focus and clarity over a wide range of conditions.

Conclusion…

Even with similar magnification range, features of the scopes are very different.

Based on the above, we can sum it up as below.  Which do you prefer…?