Before investing in wheels, I'd try to see pics of them on the M3. Or Pshop them. Whatever it takes. The pics of CSL type rims on the E9X M3 are okay, but not exceptional IMO. So, the P40s would not be high on my list. I can't say much about the P43s based on just the pic of the wheel. It'll be interesting to see what BMW does to the E92 CSL in terms of wheels because whatever they end up doing to it will most likely become the new trend.
The stock 19" wheels look great and really hard to beat (in weight and looks). The Breyton GTS Race wheels look great IMO, but are considerably heavier. Anyway, I guess I didn't exactly answer your question here...