I think in 10-20 years people will say "yeah the 1M is cool and limited production but I still want a V8 M3". Put the numbers aside, the M3 is repeatedly called the benchmark of luxury performance and handling. It has a reputation that speaks for itself and a significant following for that reason. Numbers are numbers, if that is all we cared about then we would all be driving ZO6's, GT500's, GTR's, and Vipers. There is more to the soul of an M3 then just the 0-60 or lap time. The M3 is a legend, the 1M is just the boy band of now.
Stay with the M3. Dont be tempted by the new factor. Although I will admit, I love that Valencia Orange.