In your favour, rear cameras spend much of their time recording someone following you, so there's not so much motion blur compared to front or side-facing cameras. As it happens, the M2 is better than most cameras for motion blur since it runs at a relatively high gain. The downside of cranking up the gain is that it's much noisier than most cameras, so you will lose the finer details as a result.
Since you have gone to the trouble of installing that 4.35mm lens in the M2 it would be a shame not to use it. I find ~4mm is a good focal length for a single rear-facing camera, although I'm sure others will have a different opinion.