Received my new Muhle R41 today and will use it tomorrow for the first time. My question, since it's reputed to be very aggressive, which blade should I use: Derby, Personna or Feather? I also have Astras, 7 O'clocks and Polsilvers to name a few. I've been think of using the Derby as it's not aggressive and very smooth.Or should I plug in a Feather and see what it can do? I'll have two days growth.