Probably waiting a year is a good idea. If there's any problems in the first year of production it will hopefully be fixed by next year this time.
The 991 have been out for a few short months and there are some sitting on the lots and everyone I have talked to has said that you can get 5% discount on them right now. I'm sure the same will apply to the M5 in the winter. Plus many people don't buy cars at that time of year so you might really be able to score a deal if you can be a little patient.
I am doing my homework and figuring out which car I want. I have it narrowed down to 3 cars.