I'll stay out of the big argument, but I was in the shower after the gym
thinking about what I should do in the future with the M...and for some reason another thought came to my mind about OP's question...since it seems like E9X M's are going to be the last NA M's, why don't you just leave it stock, go with bolt on's which will give you more torque, and/or in the extreme case go with stroker? Since it seems the next M3 will have a turbo engine you can get that one in the future and enjoy it then?...don't know, just a thought...
btw, I'm absolutely 50/50 on stroker vs sc...I love them both. From my experience, car's with turbo's always perform higher vs NA which have similar HP and torque numbers, but since BMW is sadly but smartly changing their future M engines to turbos, I think we should enjoy this last one as it is...NA! plus, in OP's case as in my and I'm sure many others, we don't plan to race or have THE fastest car..so no point going for slightly more performance at a slightly higher risk...