I must say that SMG II is very different compared to SMG III.. I have now M3 Cab SMG II -04 and M5 SMG III.
As a normal driver my comment is that SMG II shifts much more brutally, engaging gear with no mercy... while SMG III feels softer and more sophisticated.
While acclerating hard with SMG II it sometimes feels this can not be good for the car : ) and never felt like this with SMG III.
Still, as a experienced driver, I must admit that pocket parking is sometimes a nightmare on both of these cars... when You are really close to another car, engaging gear and moving only few centimeters can be a difficult job!
Bot II and III start with automode on startup, which I hate so much!
I think other difference is that SMG II has this uphill mode which applies when You start uphill and You press down-paddle for a second, it raises rpm a little and brakes to amke it easier to start...SMG III seems to have that on breakpaddle.
This is only after 500 km's with my new m5 ; )