I have given in and now have a Sea Dweller 4000 (Basel 2014) version. So now have three divers from Rolex. I'll try and do an in-depth comparison with my 16660 by in the meantime here are some comparison pictures:
SDc4000 vs SubNDc
and here
SDc4000 vz SD16660
camera kit
Nikon D700 FX
105mm micro-Nikkor lens
Speedlight SB-800 shot off-body