I currently drive a 306hp car. For daily commuting, there is more than plenty of power left. Only rarely using 100% of the power.
Even 200hp should be enough for the daily commute. Everything above is just fun (and in a lot of cases to show off). 540hp/795nm to be stuck in traffic? People who never had such power will probably be flashed very often, at least the first year. And when the fees become too big, or too often, you'll learn to temper your right foot.
I also started with the e40 but adding options made me choose the M50. One of them is for instance the electric seats, pretty expensive but included in the M50 and not in the e40. Add 18 or 19-inch wheels, and the two models come closer to each other price-wise. Nowadays, with the price increase of the M50, it'll be harder. Finally, the 4x4 convinced me (I now also drive a Quattro, which is so much fun).
And if you take the M Sport pack there's hardly any difference between the two (except for the mirror and the front air intakes.
I even ordered mine without the M-badges in the back and on the side, so non-BMW people would not see if it's a M50 or a e40 (see, to show off

)